Biochemistry Viva Questions

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Contents 1. Cell Organells ....................................................... 1 2. Cell Membranes: Structure and Function ....... 3 3. Amino Acids: Structure and Properties ........... 8 4. Proteins: Structure and Function .................... 17 5. Enzymology-I ..................................................... 27 6. Enzymology-II: Iso-Enzymes and Clinical Enzymology ......................................... 40 7. Methods of Separation & Purification of Biological Compounds, Methods of Study of Metabolism ......................................... 47 8. Carbohydrates-I:Chemistry, Digestion and Absorption .......................................................... 52 9. Carbohydrates-II: Major Metabolic Pathways of Glucose, Glycolysis, Gluconeogenesis, Glycogen Metabolism ...... 61 10. Carbohydrates-III: Regulation of Blood Sugar, Insulin and Diabets Mellitus .............. 70 11. Carbohydrates-IV: Other Metabolic Pathways (HMP Shunt Pathway, Fructose, Galactose, Glucuronic Acid, Alcohol) ................................ 81

2 Viva—based on Textbook of Biochemistry 12. Lipids-I: Chemistry, Digestion and Absorption of Lipids ......................................... 88 13. Lipids-II: Metabolism of Fatty acids, Fatty acid oxidation, Fatty acid synthesis, Lipolysis, Ketone bodies ..................................................... 95 14. Lipids-III: Cholesterol, Lipoproteins and Cardiovascular Diseases ................................. 103 15. Lipids-IV: MCFA, PUFA and Prostaglandins .................................................. 112 16. Lipids-V: Compound Lipids ......................... 118 17. Amino Acid Metabolism-I: General: Digestion, Absorption, Transamination, Urea ...................................... 122 18. Amino Acid Metabolism-II: Simple, Hydroxy and Sulfur Containing Amino Acids Glycine, Serine, Alanine, Threonine, Methionine, Cysteine ...................................... 128 19. Amino Acid Metabolism-III: Acidic, Basic and Branched Chain Amino Acids, Glutamic acid, Glutamine, Aspartic acid, Asparagine, Lysine, Nitric Oxide, Valine, Leucine, Isoleucine .... 132 20. Amino Acid Metabolism-IV: Aromatic Amino Acids: Phenyl alanine, Tyrosine, Tryptophan, Histidine ............................................................ 137 21. Amino Acid Metabolism-V: Inter-relations of Amino Acid Metabolisms, One Carbon Metabolism, Amino Acidurias ...................... 142

Contents

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22. Citric Acid Cycle .............................................. 144 23. Electron Transport Chain ............................... 147 24. Free Radicals and Anti-oxidants ................... 151 25. Plasma Proteins ................................................ 153 26. Immunochemistry ............................................ 156 27. Specialised Proteins: Collagen, Myosin ...... 158 28. Heme Synthesis and Breakdown ................. 160 29. Haemoglobins .................................................. 165 30. Vitamin-I: Fat Soluble Vitamins: A, D, E and K .................................................................. 169 31. Vitamin-II: Water soluble vitamins .............. 174 32. Mineral Metabolism ........................................ 189 33. Energy Metabolism and Nutrition ............... 195 34. Detoxification and Biotransformation of Xenobiotics ........................................................ 199 35. Biochemical Aspects of Environmental Pollution ............................................................ 201 36. Acid Base Balance and pH ............................. 203 37. Electrolyte and Water Balance ....................... 207 38. Molecular Biology-I: Nucleotides, Chemistry and Metabolism ............................................... 209

4 Viva—based on Textbook of Biochemistry 39. Molecular Biology-II: DNA structure and Replication ........................................................ 216 40. Molecular Biology-III: Transcription and Translation ........................................................ 220 41. Molecular Biology-IV: Molecular Genetics and Control of Gene Expression ................... 227 42. Molecular Biology-V: Recombinant DNA Technology and Gene Therapy .................... 229 43. Biochemistry of AIDS ..................................... 233 44. Biochemistry of Cancer ................................... 235 45. Applications of Radio-isotopes in Medicine ............................................................ 238 46. Body Fluids ....................................................... 240 47. Hormones-I: Mechanism of Action of Hormones .......................................................... 242 48. Hormones-II: Pituitary Hormones ................ 244 49. Hormones-III: Steroid Hormones ................. 246 50. Hormones-IV: Thyroid Hormones ............... 248 51. Clinical Biochemistry-I: .................................. 250 52. Clinical Biochemistry-II: Liver and Gastric Function Tests ..................................... 252 53. Clinical Biochemistry-III: Kidney Function Tests .................................................................... 256

Cell Organelles

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Cell Organelles

Q. What is the function of Golgi complex? A. Maturation and processing of nascent proteins, glycosylation of proteins, secretion newly synthesised proteins (Page 3). Q. What is the function of endoplasmic reticulum? (Page 3) A. Biosynthesis of proteins, drug metabolism, desaturation of fatty acids. Q. What is the marker enzyme for endoplasmic reticulum? A. Glucose-6-phosphatase (Page 3, Table 1.3). Q. Where does protein synthesis take place? A. On the walls of endoplasmic reticulum and also in cytosol (Page 3). Q. What are cathepsins? A. They are intracellular proteolytic enzymes (Page 4).

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Viva—based on Textbook of Biochemistry

Q. What is the function of lysosomes? A. They are bags of hydrolytic enzymes that bring about degradation of macromolecules (Page 4). Q. What is lysozyme? A. It is an enzyme present in external secretions (Page 35). Q. What are peroxisomes? A. They contain peroxidase and catalase, necessary for destroying the unwanted free radicals. (Page 4) Q. What are the important metabolic events taking place in cytoplasm? A. Glycolysis (Embden-Meyerhof pathway), HMP shunt pathway, glycogen metabolism, Fatty acid synthesis, Synthesis of nucleotides, Degradation of amino acids (See Page 5, Table 1.4). Q. What is the function of mitochondria? A. Generation of ATP (See page 5). Q. What are the important metabolic events taking place in mitochondria? A. TCA cycle, electron transport chain, beta oxidation of fatty acids and urea cycle (Page 5).

Cell Membranes; Structure and Function

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Cell Membranes: Structure and Function Q. What are ecto-enzymes? A. They are enzymes seen on the outer part of cell membrane (Page 6). Q. Give examples of ecto-enzymes. A. Alkaline phosphatase, 5’nucleotidase

(Page 6).

Q. How do you describe the structure of cell membrane? A. Fluid mosaic model (Page 6). Q. What are the characteristics of fluid mosaic model?. A. Membrane is composed of lipid bilayer. Phospholipids are arranged in bilayers with a hydrophobic core (Page 6). Q. What do you mean by fluidity of the membrane? A. The lipid bilayer shows free lateral movement of its components; but flip-flop movement is restricted (Page 6).

4 Viva—based on Textbook of Biochemistry Q. What are the components of membrane that alter the fluidity? A. Cholesterol and unsaturated fatty acids (Page 6). Q. What are the different types of transport mechanisms? A. Passive and active. Passive type is subclassified as simple diffusion and facilitated diffusion (Page 8). Q. What are the salient features of facilitated diffusion? A. It is carrier mediated. It does not require energy directly (Page 8). Q. Can you give an example of facilitated transport? A. Glucose transporters (Page 8). Q. What are ion channels? A. They are special devices for quick transport of electrolytes (Page 9). Q. Give some examples of ion channels. A. Ion channels specific for calcium, potassium and chloride (Page 9). Q. What are ionophores? A. They are transport antibiotics which increase the permeability of membrane to ions, e.g. valinomycin, gramicidin (Page 10). Q. What are the salient features of active transport? A. It requires transporters. It requires energy. Transport is generally unidirectional (Page 10).

Cell Membranes; Structure and Function

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Q. Give examples of active transport systems. A. Sodium pump, calcium pump (Page 10). Q. What is the importance of sodium pump? A. Cell has low intracellular sodium; but concentration of potassium inside the cell is high; this is maintained by sodium pump. About 40% of the total energy expenditure in a cell is used for this active transport system (Page 10). Q. How does sodium pump work? A. It is called sodium-potassium activated ATPase. Hydrolysis of one molecule of ATP can result in expulsion of 3 sodium ions and influx of 2 potassium ions (Page 10). Q. What is its clinical significance? A. Digoxin increases the contractility of the cardiac muscle, by inhibiting the sodium pump (Page 10). Q. What is a uniport? A. It carries single solute across the membrane (Page 10). Q. Give examples of uniport. A. Glucose transporter (GluT2) operating in most of the cells is an example. Calcium pump is another example (Page 10). Q. What is co-transport? A. If transfer of one molecule depends on simultaneous or sequential transfer of another molecule, it is called co-transport system (Page 10).

6 Viva—based on Textbook of Biochemistry Q. How are co-transport systems classified? A. The cotransport system may be symport or antiport (Page 10). Q. What is symport? A. In symport, the transporter carries two solutes in the same direction across the membrane (Page 10). Q. Give examples of symport. (Page 10) A. Sodium dependent glucose transporter (SgluT) (Fig.8.31). Phlorhizin, an inhibitor of sodium-dependent cotransport of glucose, especially in the proximal convoluted tubules of kidney, produces renal damage and results in renal diabetes. Amino acid transport is another example for symport. Q. What is antiport system?. (Page 10) A. The antiport system carries two solutes or ions in opposite direction. Q. Give examples of antiport. (Page 10) A. Sodium pump (Fig.2.7) or chloride-bicarbonate exchange in RBC (Fig.29.4). Q. What is endocytosis?. (Page 11) A. It is the mechanism by which cells internalise extracellular macromolecules. Q. What is pinocytosis?. (Page 11) A. It is receptor mediated. Low Density Lipoprotein (LDL) binds to the LDL receptor and the complex is later internalised. These vesicles are coated with Clathrin. .

Cell Membranes; Structure and Function

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Q. What is phagocytosis. (Page 11) A. It is the engulfment and internalisation of large particles such as bacteria by macrophages and granulocytes. Q. What is respiratory burst. (Page 11) A. During phagocytosis, there is an increase in oxygen consumption with formation of the superoxide ion.

8 Viva—based on Textbook of Biochemistry

Amino Acids: Structure and Properties Q. How do you classify amino acids? (Page 12) A. Based on the structure, amino acids are classified into: Simple amino acids, Branched chain amino acids, Hydroxy amino acids, Sulfur containing amino acids, Amino acids with amide group, Acidic amino acids, Basic amino acids, Aromatic amino acids, Heterocyclic amino acids, Imino acid and Derived amino acids. Q. What are branched chain amino acids?(Page 12) A. Valine, leucine and isoleucine. Q. What are hydroxy amino acids? A. Serine and threonine.

(Page 12)

Q. Name the Sulfur containing amino acids. (Page 12) A. Cysteine and methionine. Q. Name the acidic amino acids. A. Aspartic acid and glutamic acid.

(Page 12)

Amino Acids: Structure and Properties

Q. What are the basic amino acids? A. Lysine and arginine.

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(Page 12)

Q. Which amino acid has a net positive charge at physiological pH? (Page 12) A. Arginine and lysine. Q. Amino acid containing a thio-ether bond is. (Page 12) A. Methionine. Q. Give examples of amino acids with hydrophobic side chains. (Page 12) A. Valine, leucine, isoleucine. Q. Give the names of aromatic amino acids. (Page 12) A. Phenylalanine and tyrosine. Q. What are heterocyclic amino acids? A. Tryptophan and histidine.

(Page 12)

Q. Give an example of an imino acid. A. Proline.

(Page 12)

Q. Give examples of derived amino acids.(Page 12) A. Hydroxy proline, hydroxy lysine, ornithine, citrulline, homocysteine. Q. Arginine contains which special group? (Page 12) A. Guanidinium group (-NH-CNH-NH2). Q. Benzene group is present in which amino acid? (Page 12) A. Phenyl alanine.

10 Viva—based on Textbook of Biochemistry Q. Phenol group is present in which amino acid? (Page 12) A. Tyrosine. Q. Tryptophan contains what special group? (Page 12) A. Indole group. Q. Which special group is present in Histidine? (Page 12) A. Imidazole group. Q. Name some hydrophobic amino acids.(Page 12) A. Valine, leucine and isoleucine. Q. Pyrrolidine group is present in which amino acid? (Page 12) A. Proline. Q. Hydrophobic bonds are formed in protein between which amino acids? A. Valine, leucine and isoleucine residues.(Page 12) Q. What is the basis of classification of amino acids into ketogenic and glucogenic? (Page 12 and 13) A. Ketogenic amino acids enter into the metabolic pathway of fats, while glucogenic amino acids enter the pathway of glucose metabolism. Q. Name a purely ketogenic amino acid.

(Page 12)

A. Leucine. Q. Name some glucogenic amino acids. A. Glycine; serine; aspartic acid.

(Page 13)

Amino Acids: Structure and Properties

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Q. Which amino acid is synthesised after it gets incorporated into the protein? A. Hydroxyproline (Page 12). Q. What are essential amino acids? (Page 13) A. They cannot be synthesized in the body; and so, they are to be provided in the diet. Q. How many amino acids are essential? (Page 13) A. Eight amino acids are essential; two are semi-essential and the rest 10 are non-essential. Q. Are non-essential amino acids necessary for the body? A. They are also necessary for protein synthesis, but they can be synthesized by the body and need not be essentially present in the diet (Page 14). Q. Name any three essential amino acids. (Page 13) A. Isoleucine, leucine, threonine. Q. Is phenyl alanine an essential amino acid? (Page 13) A. Yes. Q. What about Tyrosine? (Page 13) A. Tyrosine is non-essential, it is synthesized from phenyl alanine. Q. Name the semi-essential amino acids. (Page 14) A. Histidine and arginine. Q. Why are they called semi-essential? (Page 14) A. Because growing children require them in food. But they are not essential for the adult individual.

12 Viva—based on Textbook of Biochemistry Q. What is iso-electric point?. (Page 14) A. The pH at which the molecule carries no net charge is called iso-electric point. Q. What are the characteristic features of iso-electric pH. (Page 14) A. At iso-electric point the amino acid will carry no net charge, there is no mobility in electrical field, solubility will be minimum, the tendency for precipitation will be maximum Q. What is the speciality of Histidine? (Page 14) A. The pK value of Histidine is 6.1, and therefore effective as a buffer at the physiological pH of 7.4. The buffering capacity of plasma proteins and hemoglobin is mainly due to histidine residue. Q. Which is the amino acid having maximum buffering capacity at physiological pH? (Page 14) A. Histidine. Q. Which amino acid is optically inactive?

(Page 15)

A. Glycine. Q. What are the isomers of amino acids? (Page 16) A. D and L varieties. Q. What are natural amino acids? (Page 16) A. Only L amino acids are seen in large quantities in nature.

Amino Acids: Structure and Properties

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Q. Can you name some substances where D-amino acids are seen? A. D-amino acids are seen in cell walls of micro-organisms and as constituents of certain antibiotics such as gramicidin-S, polymyxin, actinomycin-D and valinomycin (Page 16). Q. What is meant by decarboxylation of an amino acid? (Page 16) A. The carboxyl group is removed from the amino acids to form the corresponding amine (Fig.3.8). Q. Give examples of decarboxylation reactions. (Page 16) A. Histidine to histamine; tyrosine to tyramine; tryptophan to tryptamine. Q. What is produced when Glutamic acid is decarboxylated? (Page 16) A. Gamma amino butyric acid or GABA. Q. What is glutamine? A. That is the amide of glutamic acid.

(Page 16)

Q. What is an amide? (Page 16) A. The extra carboxyl group (other thanÿalpha carboxyl) can combine with ammonia to form the corresponding amide. Q. How asparagines is produced? (Page 16) A. Aspartic acid + ammonia will form asparagine. Q. What is transamination? (Page 16) A. The alpha amino group of amino acid can be transferred to alpha keto acid to form the corresponding new amino acid and alpha keto acid (Fig.3.10).

14 Viva—based on Textbook of Biochemistry Q. Give an example of transamination reaction. (Page 16) A. Glutamic acid + pyruvic acid alpha keto glutarate + alanine. Q. What is the product of transamination reaction of pyruvate with glutamate? A. Alanine and alpha keto glutarate (Page 16). Q. What is the biological significance of transamination reaction? A. These are important for the interconversion of amino acids. Non-essential amino acids are synthesized by this process (Page 16). Q. What is the clinical significance of transaminases? (Page 16) A. Transaminases in blood are elevated in liver and heart diseases. Q. What is the significance of SH groups in proteins? (Page 17) A. The SH group of cysteine can form a disulfide (SS) bond with another cysteine residue. The two cysteine residues can connect two polypeptide chains by the formation of interchain disulfide bonds. Q. Glutathione is made up of which amino acids? (Page 17) A. Glutamic acid, cysteine and glycine. Q. Phosphorylation is taking place on which amino acid residue? A. Serine (Page 17).

Amino Acids: Structure and Properties

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Q. What is ninhydrin reaction? (Page 18) A. All amino acids when heated with ninhydrin will give a pink colour. Q. What is the importance of ninhydrin reaction? (Page 18) A. It is used for qualitative test and quantitative estimation of amino acids. It is often used for detection of amino acids in chromatography. Q. Do proteins give a color with ninhydrin? (Page 18) A. Proteins do not give a true color reaction; but Nterminal end amino group of protein will react with ninhydrin, to produce a blue color. Q. What is biuret reaction? (Page 18) A. Cupric ions in alkaline medium form a violet colour with peptide bond nitrogen. Q. Will amino acids give a positive biuret test? (Page 18) A. No. This needs a minimum of two peptide bonds. Q. What is the use of biuret reaction? (Page 18) A. This reaction can be used for qualitative identification and quantitative estimation of proteins. Q. What is biuret? (Page 18) A. The name is derived from the compound biuret, a condensation product of two urea molecules, which also gives a positive color test.

16 Viva—based on Textbook of Biochemistry Q. What is the basis of xanthoproteic test?

(Page 18) A. The ring systems in phenyl alanine, tyrosine and tryptophan will answer this test.

Q. The protein which does not answer the aldehyde test is. (Page 18) A. Gelatin.

Proteins: Structure and Function

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Proteins: Structure and Function Q. How proteins are made up of? (Page 19) A. Proteins are made by polymerisation of amino acids through peptide bonds. Q. What is a peptide bond? (Page 19) A. Alpha carboxyl group of one amino acid reacts with alpha amino group of another amino acid to form a peptide bond or CO-NH bridge (Fig. 4.1). Q. What is a dipeptide? (Page 19) A. Two amino acids are combined to form a dipeptide. Q. How many peptide bonds are present in a tripeptide? (Page 19) A. A tripeptide is a combination of three amino acids; so there are two peptide bonds. Q. What is a polypeptide? (Page 19) A. A combination of 10 to 50 amino acids is called as a polypeptide.

18 Viva—based on Textbook of Biochemistry Q. What is the difference between a polypeptide and a protein? (Page 19) A. A combination of 10 to 50 amino acids is called a polypeptide. By convention, chains containing more than 50 amino acids are called proteins. Q. What are the levels of organizations of proteins? (Page 19) A. Proteins have primary, secondary, tertiary and quaternary levels of organisation. Q. What is meant by primary structure of a protein? (Page 19) A. It denotes the number and sequence of amino acids in the protein. Q. What is the force that maintains the primary structure? (Page 19) A. The primary structure is maintained by the covalent bonds of the peptide linkages (Fig. 4.2). Q. What are the salient features of a peptide bond? (Page 19) A. The peptide bond is a partial double bond. The C-N bond is ‘trans’ in nature and there is no freedom of rotation because of the partial double bond character. Q. What is the N-terminal end of a protein? (Page 20) A. In a protein, at one end there will be one free alpha amino group. This end is called the amino terminal (N-terminal) end and the amino acid contributing the ?-amino group is named as the first amino acid.

Proteins: Structure and Function

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Q. What are the names for the end amino acids of proteins. (Page 20) A. The end where there is a free alpha amino group is called the amino terminal (N-terminal) end. The other end of the polypeptide chain is called the carboxy terminal end (C-terminal) where there is a free alpha carboxyl group. Q. Can you give an example of a pseudopeptide? (Page 20) A. Glutathione (gamma-glutamyl-cysteinyl-glycine). The pseudopeptide a peptide bond formed by carboxyl group, other than that of alpha position. Q. What are the salient structural features of insulin? (Page 20) A. It has two polypeptide chains. These chains are held together by disulfide bridges. Insulin has total 51 amino acids. Q. What is pro-insulin? (Page 20) A. Insulin is synthesised by the beta cells of pancreas as a prohormone, proinsulin is a single poly-peptide chain with 86 amino acids. Q. What is mutation? (Page 20) A. Amino acid change in the linear sequence is called a mutation. Q. Can you give an example? (Page 20) A. sickle cell anemia due to Haemoglobin S, Q. What is the defect in HbS? (Page 20) A. Normally the 6th amino acid in the beta chain is glutamic acid, this is replaced by valine in the HbS molecule.

20 Viva—based on Textbook of Biochemistry Q. Which are the forces that maintain the secondary, tertiary and quaternary structures of a protein? (Page 21) A. Hydrogen bonds, Electrostatic bonds, Van der Waal’s forces and Hydrophobic bonds. Q. What are the salient features of alpha structure of proteins? (Page 22) A. It is a right-handed spiral structure; each turn is formed by 3.6 amino acid residues; it is major structural motif in globular proteins. Q. Which will inhibit the formation of alpha helix? (Page 22) A. Proline. Q. What is meant by secondary structure of a protein? (Page 22) A. Secondary structure denotes the configurational relationship between residues which are about 34 amino acids apart. In other words, secondary level defines the organisation at immediate vicinity of amino acids. Q. What is meant by tertiary structure of a protein? (Page 22) A. The tertiary structure denotes three dimensional structure of the whole protein. It defines the steric relationship of amino acids which are far apart from each other in the linear sequence. Q. What is meant by a domain of a protein? (Page 22) A. It is the term used to denote a compact unit of a protein. It generally represents a functional unit.

Proteins: Structure and Function

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Q. What is meant by quaternary structure of a protein? (Page 22) A. Certain polypeptides will aggregate to form one functional protein. This is referred to as the quaternary structure. Q. Give some examples of proteins having quaternary structure. (Page 23) A. Hemoglobin, lactate dehydrogenase, immunoglobulin. Q. What are the reagents that are used for identifying the first amino acid in a protein? (Page 24) A. Fluoro dinitro benzene, dansyl chloride, phenyl iso thio cyanate. Q. Protein chains may be separated by what reagent? (Page 24) A. 8 molar urea. Q. What is meant by Ingram’s technique?(Page 24) A. Protein digestion by trypsin, followed by two dimensional chromatography. Q. It is otherwise known as what? (Page 24) A. Finger printing of proteins or peptide mapping. Q. Secondary structure of protein can be studied by what methods? (Page 25) A. X-ray diffraction study, optical rotatory dispersion, and nuclear magnetic resonance (NMR). Q. What is iso-electric point of a protein? (Page 25) A. At the iso-electric point, the number of anions and cations present on the protein molecule will be equal and the net charge is zero.

22 Viva—based on Textbook of Biochemistry Q. What are the characteristic features of iso-electric point? (Page 25) A. At the pI value, the proteins will not migrate in an electrical field; solubility, buffering capacity and viscosity will be minimum and precipitation will be maximum. Q. What is the iso-electric pH of human albumin? (Page 25) A. It is 4.7. Q. How proteins are precipitated from solution? (Page 25) A. Any factor which neutralises the charge or removes water of hydration will cause precipitation of proteins. Q. How albumin is precipitated? (Page 25) A. By full saturation of ammonium sulfate or 28 % sodium sulfate. Q. What will be precipitated by half-saturation of ammonium sulfate? (Page 25) A. Globulins are precipitated by half-saturation of ammonium sulfate. Q. Give an example of precipitation at iso-electric point. (Page 26) A. Casein is precipitated when the solution is brought to iso-electric pH. Q. What is the iso-electric pH of casein? (Page 26) A. 4.6.

Proteins: Structure and Function

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Q. Give some examples of anionic precipitating agents. (Page 26) A. Tungstic acid, phosphotungstic acid, trichloro acetic acid, picric acid, sulphosalicylic acid and tannic acid are protein precipitating agents. Q. What are the features of denaturation?(Page 26) A. The secondary, tertiary and quaternary structures are lost, but primary structure is preserved. The functional activity is lost. The denature proteins are insoluble and easily precipitated. Q. What are the usual agents that cause denaturation of proteins? (Page 26) A. Brief heating, urea, X-ray, ultraviolet ray, high pressure, vigorous shaking. Q. What is heat coagulation? (Page 26) A. When heated at iso-electric point, some proteins will denature irreversibly to produce thick floating conglomerates called coagulum. This is called heat coagulation. Q. Give examples of proteins that coagulate easily. (Page 26) A. Albumin is easily coagulated, and globulins to a lesser extent. Q. How proteins are classified? (Page 27) A. They may be classified depending on the function or based on the physicochemical characteristics or based on their nutritional value.

24 Viva—based on Textbook of Biochemistry Q. What is the functional classification of proteins? (Page 27) A. 1. Catalytic proteins, 2. Structural proteins, 3. Contractile proteins, 4. Transport proteins, 5. Regulatory proteins or hormones, 6. Genetic proteins, and 7. Protective proteins. Q. Based on physiochemical properties, how are they classified? (Page 27) A. Simple proteins, conjugated proteins and derived proteins. Q. Give examples of simple proteins. (Page 27) A. Albumins, globulins, protamines, prolamines, lectins, scleroproteins. Q. Give examples of scleroproteins. (Page 27) A. Collagen of bone, cartilage and tendon, keratin of hair, horn, nail and hoof. Q. What are conjugated proteins? (Page 27) A. Combinations of protein with a non-protein part is called prosthetic group. Q. How are conjugated group subclassified? (Page 27) A. Glycoproteins, lipoproteins, nucleoproteins, chromoproteins, phospho-proteins and metallo-proteins. Q. Give some examples of chromoproteins. (Page 27) A. Hemoglobin, flavoproteins, visual purple.

Proteins: Structure and Function

Q. Give examples of phosphoproteins.

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(Page 27)

A. Casein of milk and vitellin of egg yolk. Q. Where is this phosphate attached to proteins? (Page 27) A. The phosphoric acid is added to the hydroxyl groups of serine and threonine residues of proteins. Q. What are lectins? (Page 27) A. Plant proteins having specific carbohydrate binding site. Q. Give an example of a nutritionally rich protein (first class protein). (Page 28) A. Casein. Q. Some proteins are called as poor proteins; why? (Page 28) A. They lack in many essential amino acids and a diet based on these proteins will not even sustain the body weight. Q. Give an example of nutritionally poor protein. (Page 28) A. Zein from corn lacks tryptophan and lysine. Q. Which method of protein estimation is dependent on the intact peptide bond? A. Biuret method. (Page 28)

26 Viva—based on Textbook of Biochemistry Q. What is the advantage of biuret method? (Page 28) A. The biuret method is simple one step process, and is the most widely used method for plasma protein estimations. Q. What is the disadvantage of biuret method? (Page 28) A. The sensitivity of the method is less and is unsuitable for estimation of proteins in milligram or microgram quantities. Q. What is the basis of Lowry’s method of protein estimation? (Page 28) A. This is based on the reduction of folin-ciocalteau phenol reagent (phosphomolybdic acid and phosphotungstic acid) by the tyrosine and tryptophan residues of protein. Q. Which component of the protein absorb UV light at 280 nm? (Page 28) A. Indole ring of tryptophan. Q. What is nephelometry? (Page 29) A. Nephelometry is defined as the detection of light scattered by turbid particles in solution.

Enzymology-I

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Enzymology-I Q. How are enzymes classified? (Page 30) A. They are classified into five major classes. Q. What are those classes? (Page 30) A. Oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Q. What is the function of oxidoreductases? (Page 30) A. Transfer of hydrogen. Q. Give an example of oxidoreducatase. (Page 30) A. Alcohol dehydrogenase. Q. What is the function of transferases? (Page 31) A. Transfer of groups other than hydrogen. Q. Give an example of transferase. A. Hexokinase.

(Page 31)

Q. What is the function of hydrolases? A. Cleave bond after adding water.

(Page 31)

28 Viva—based on Textbook of Biochemistry Q. Give an example of a hydrolase. A. Acetyl choline esterase.

(Page 31)

Q. Peptidases are classified under which class of enzyme? (Page 31) A. Hydrolases. Q. What is the function of lyases? A. Cleave bond without adding water.

(Page 31)

Q. Which enzyme will add water to a double bond, without breaking the bond? A. Hydratase. (Page 31) Q. Give an example of lyase. A. Aldolase.

(Page 31)

Q. Give an example of isomerase. A. Triose phosphate isomerase.

(Page 31)

Q. What is the function of ligases? (Page 31) A. ATP dependent condensation of two molecules. Q. What is the difference between synthase and synthetase? (Page 31) A. Synthetases are ATP-dependent enzymes catalysing biosynthetic reactions; they belong to Ligases. Synthases are enzymes catalysing biosynthetic reactions; but they do not require ATP directly; they belong to classes other than Ligases. Q. Give examples of synthetases. (Page 31) A. Carbamoyl phosphate synthetase, arginino succinate synthetase, PRPP synthetase, glutamine synthetase.

Enzymology-I

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Q. Give examples of synthases. (Page 31) A. Glycogen synthase, ALA synthase, IMP synthase. Q. What are co-enzymes? (Page 31) A. Enzyme may contain a non-protein part, the coenzyme. The co-enzyme is essential for the biological activity of the enzyme. A co-enzyme is a low molecular weight organic substance, without which the enzyme cannot exhibit any reaction. Coenzyme accepts one of the products of the reaction; and so act as a co-substrate. Q. What is holo-enzyme? (Page 31) A. When apo-enzyme and co-enzymes are added, holo-enzyme is produced. Fully active enzyme is called Holo-enzyme. Q. How are co-enzymes classified? (Page 31) A. (a) Those taking part in reactions catalysed by oxidoreductases by donating or accepting hydrogen atoms or electrons. (b) Those co-enzymes taking part in reactions transferring groups other than hydrogen. Q. Give some examples of co-enzymes involved in oxidoreductases. (Page 31) A. NAD, NADP, FAD. Q. What is the full form of NAD? A. Nicotinamide adenine dinucleotide.

(Page 32)

Q. What is FAD? A. Flavin adenine dinucleotide.

(Page 32)

30 Viva—based on Textbook of Biochemistry Q. Give some examples of co-enzymes involved in reactions other than hydrogen transfer. (Page 32) A. Thiamine pyrophosphate, pyridoxal phosphate, biotin, co-enzyme A, ATP. Q. What is the full form of ATP? A. Adenosine triphosphate.

(Page 32)

Q. What is the function of ATP? (Page 32) A. It is the energy currency in the body. During the oxidation of food stuffs, energy is released, a part of which is stored as chemical energy in the form of ATP. Other reaction requiring energy are coupled with ATP. Q. Name the enzymes containing copper.(Page 33) A. Superoxide dismutase, tyrosinase, cytochrome oxidase. Q. Which metal is required for the action of Kinases? (Page 33) A. Magnesium. Q. Chloride ions activate which enzyme? (Page 33) A. Amylase. Q. Which enzyme contains molybdenum? (Page 33) A. Xanthine oxidase. Q. Name some iron containing enzymes. (Page 33) A. Cytochrome oxidase, catalase, peroxidase, xanthine oxidase.

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Q. What is Michaelis-Menten Theory ? (Page 33) A. It is otherwise called enzyme-substrate complex theory. The enzyme combines with the substrate, to form an enzyme-substrate complex, which immediately breaks down to the enzyme and the product. Q. What is Fischer’s theory? (Page 34) A. It states that the three dimensional structure of the active site of the enzyme is complementary to the substrate. Thus, enzyme and substrate fit each other like a key and its lock. Q. What is Koshland’s induced fit theory? (Page 34) A. The substrate induces conformational changes in the enzyme, such that precise orientation of catalytic groups is effected. Q. What is active site of an enzyme? (Page 35) A. That area of the enzyme where catalysis occurs is referred to as active site or active center. Q. What is meant by serine proteases? (Page 35) A. Proteases (proteolytic enzymes) having a serine residue at its active center. Q. Give an example of a serine protease. (Page 35) A. Trypsin, chymotrypsin, thrombin. Q. Thermodynamically, how reactions are classified? (Page 36) A. Exothermic, isothermic and endothermic reactions.

32 Viva—based on Textbook of Biochemistry Q. What is exothermic reaction? (Page 36) A. Here energy is released from the reaction, and therefore reaction essentially goes to completion, e.g. urease enzyme, converting urea to ammonia + CO2 + energy. Q. What is endergonic reaction? (Page 36) A. Energy is consumed and external energy is to be supplied for these reactions. In the body this is usually accomplished by coupling the endergonic reaction with an exergonic reaction, e.g. Hexokinase reaction, Glucose + ATP ® Glucose-6-Phosphate + ADP. Q. What are the salient features of enzyme kinetics? (Page 36) A. Enzymes lower activation energy. They increase the chemical reaction, but do not alter equilibrium of the reaction. Q. What are the factors influencing enzyme reaction? (Page 36) A. Enzyme concentration, substrate concentration, product concentration, temperature, pH and presence of activators or inhibitors. Q. What is Km value? (Page 37) A. Substrate concentration (expressed in moles/L) at half-maximal velocity is the Km value. Q. What does it indicate? (Page 37) A. It denotes that 50% of enzyme molecules are bound with substrate molecules at that particular substrate concentration

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Q. What is its significance? (Page 37) A. Km is independent of enzyme concentration. Km value is thus constant for an enzyme. It is the characteristic feature of a particular enzyme for a specific substrate. Km denotes the affinity of enzyme to substrate. Thus, the lesser the numerical value of Km, the affinity of the enzyme for the substrate is more. Q. What is the use of assessing the Km value of an enzyme? What is the application? (Page 38) A. Determination of Km value is also useful to understand the natural substrate of an enzyme. Study of Km value will also differentiate the competitive and non-competitive inhibitions. Q. What is the effect of temperature on enzyme velocity? (Page 39) A. The velocity of reaction increases when temperature is increased, reaches a maximum and then falls (Bell-shaped curve) Q. Why it falls? (Page 39) A. when temperature is more than 50ºC, heat denaturation and consequent loss of tertiary structure of protein occurs. Q. What is the effect of pH on the activity of an enzyme? (Page 39) A. Each enzyme has an optimum pH, on both sides of which the velocity will be drastically reduced. The graph will show a bell-shaped curve.

34 Viva—based on Textbook of Biochemistry Q. What is the explanation for the effect of pH? (Page 39) A. The pH decides the charge on the amino acid residues at the active site. The net charge on the enzyme protein would influence substrate binding and catalytic activity. Q. What is the optimum pH of usual enzymes? (Page 39) A. Usually enzymes have the optimum pH between 6 and 8. Q. Are there any important exceptions for this general rule? (Page 39) A. Pepsin (optimum pH 1-2), alkaline phosphatase (optimum pH 9-10) and Acid phosphatase (4-5). Q. What is zymogen? (Page 39) A. It is otherwise called pro-enzyme. Inactive zymogen is activated by removal of a piece of the pro-enzyme. Q. Give an example of zymogen is activated? (Page 39) A. By splitting a single peptide bond, and removal of a small polypeptide from trypsinogen, the active trypsin is formed. This results in unmasking of the active centre.

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Q. What is the significance of zymogen activation? (Page 39) A. Gastro-intestinal enzymes are synthesised in the form of pro-enzymes, and only after secretion into the alimentary canal, they are activated. This prevents autolysis of cellular structural proteins. Coagulation factors are seen in blood as zymogen form, their activation takes place only when necessity arises. This prevents intravascular coagulation. Q. What are the different types of inhibitions of enzyme activity? (Page 39) A. Competitive inhibition, non-competitive inhibition, suicide inhibition, and allosteric regulation. Q. What are salient features of competitive inhibition? (Page 40) A. Competitive inhibitor is a structural analogue. 2. It is reversible. 3. Km is increased. 4. Vmax is not changed. Q. Give examples of competitive inhibition. (Page 40) A. Malonate inhibits succinate dehydrogenase. Q. Give examples of clinical application of competitive inhibition. (Page 40) A. Sulfonamide inhibits PABA incorporation in bacteria, and so acts as an antibacterial agent. Methotrexate inhibits folate reductase system, dicoumarol inhibits vitamin K.

36 Viva—based on Textbook of Biochemistry Q. What is the immediate treatment for methanol poisoning? (Page 41) A. Methanol is oxidised by alcohol dehydrogenase to formaldehyde which causes the acute toxicity. Antidote to methanol poisoning is ethanol which is the natural substrate for alcohol dehydrogenase. So ethanol is preferentially utilised. Q. What are the salient features of non-competitive inhibition? (Page 41) A. Non-competitive inhibitor has no structural similarity with the substrate. 2. It is generally not reversible 3. Km is not changed. 4. Vmax is reduced. Q. Give examples of non-competitive inhibition. (Page 41) A. Di-isopropyl fluoro phosphate inhibits trypsin, fluoride inhibits and enolase. Q. Iodo-acetate inhibits enzyme by reacting with which group at the active site of the enzyme? (Page 41) A. Sulfhydryl group. Q. What is the mechanism of inhibitory action of Di-isopropyl fluoro phosphate? (Page 41) A. It inhibits enzymes with serine in their active centres, e.g. acetylcholine esterase. Q. What is suicide inhibition? (Page 42) A. In suicide inhibition, the structural analogue is converted to a more effective inhibitor with the help of the enzyme to be inhibited. The inhibitor makes use of the enzyme’s own reaction mechanism to inactivate it.

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Q. What is the other term for suicide inhibition? (Page 42) A. Mechanism based inactivation. Q. Give examples for suicide inhibition. (Page 42) A. Ornithine decarboxylase (ODC) is inhibited by difluro methyl ornithine (DFMO). Another example is Allopurinol which is oxidised by xanthine oxidase to alloxanthine that is a strong inhibitor of xanthine oxidase. Q. What is allosteric inhibition? (Page 42) A. Allosteric enzyme has one catalytic site where the substrate binds and another separate allosteric site where the modifier binds. Q. What are the salient features of allosteric inhibition? (Page 43) A. (1) The inhibitor is not a substrate analogue. (2) It is partially reversible when excess substrate is added. (3) Km is usually increased. (4) Vmax is reduced. (5) Most allosteric enzymes possess quaternary structure. They are made up of subunits. Q. Give examples for allosteric inhibition. (Table 5.7) A. ALA synthase, aspartyl trans-carbamoylase, HMG CoA reductase Q. What is covalent modification? (Page 43) A. It means, either addition of a group to the enzyme protein by a covalent bond; or removal of a group by cleaving a covalent bond.

38 Viva—based on Textbook of Biochemistry Q. Give some examples of covalent modification. (Page 44) A. Glycogen synthase is inactive, in the phosphorylated state, whereas glycogen phosphorylase is active when phosphorylated. Q. What is meant by induction? (Page 44) A. Induction is effected at the level of DNA. The inducer will relieve the repression on the operator site and will remove the block on the biosynthesis of the enzyme molecules. Q. Give an example of induction. (Page 44) A. Induction of lactose-utilising enzymes in the bacteria when the media contains lactose in the absence of glucose. In humans, Tryptophan pyrrolase and transaminases are induced by glucocorticoids. Glucokinase is induced by glucose. ALA synthase is induced by barbiturates. Q. What are constitutive enzymes? (Page 44) A. Enzymes whose concentration in a cell is independent of inducer are called constitutive enzymes. Q. What is repression? (Page 44) A. Repression acts at the gene level, the number of enzyme molecules is reduced in the presence of repressor molecule. Q. Give an example of repression. (Page 44) A. The key enzyme of heme synthesis, ALA synthase is autoregulated by the heme by means of repression.

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Q. Give examples of multi-enzyme complexes. (Page 44) A. Fatty acid synthase, pyruvate dehydrogenase, and alpha keto glutarate dehydrogenase. Q. What are the types of specificity shown by enzymes? (Page 45) A. Absolute specificity, group specificity and streospecificity. Q. Give an example for absolute specificity. (Page 45) A. Urea is the only substrate for urease. Q. Give an example for group specificity. (Page 45) A. trypsin can hydrolyse peptide bonds formed by carboxyl groups of arginine or lysine residues.

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Viva—based on Textbook of Biochemistry

Enzymology-II

Iso-Enzymes and Clinical Enzymology Q. What are iso-enzymes? (Page 46) A. They are physically distinct forms of the same enzyme activity. They have identical catalytic properties, but differ in structure. Q. How to differentiate iso-enzymes. (Page 46) A. Electrophoresis, heat stability, km value, inhibitor specificity, and tissue localization. Q. Which is a functional enzyme in plasma? (Page 46) A. They are actively secreted into plasma, and have some functions in the blood. For example, enzymes of blood coagulation. Q. What is non-functional enzymes in plasma? (Page 46) A. They are coming out from cells due to normal wear and tear.

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Q. What is their clinical significance? (Page 46) A. Their normal levels in blood are very low, but are drastically increased during cell death (necrosis) or disease. Therefore, assays of these enzymes are very useful in diagnosis of diseases. Q. Lactate dehydrogenase has how many polypeptide subunits? (Page 47) A. Four. It is a tetramer. Q. Lactate dehydrogenase has how many iso-enzymes? (Page 47) A. Five Q. What are they? (Page 47) A. H4, H3M, H2M2, M3H and M4 varieties, forming five iso-enzymes. All these five forms are seen in all persons. Q. How do you separate LDH iso-enzymes in laboratory? (Page 47) A. By cellulose acetate electrophoresis at pH 8.6. Q. LDH level in blood is increased in which conditions? (Page 47) A. Myocardial infarction, hemolytic anemias, muscular dystrophy, carcinomas, leukemias, and any condition which causes necrosis of body cells. Q. How do you further investigate for myocardial infarction? (Page 47) A. LDH-1 (H4) iso-enzyme is increased.

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Q. What is flipped pattern? (Page 47) A. Normally LDH-2 (H3M1) concentration in blood is greater than LDH-1 (H4), but this pattern is reversed in myocardial infarction, this is called flipped pattern. Q. What are the serum enzymes helpful in the diagnosis of myocardial infarction? A. Lactate dehydrogenase (LDH) H4 iso-enzyme, creatine kinase (CK) CK MB iso-enzyme and aspartyl transaminase (AST). Q. Creatine kinase (CK) level in serum is increased in which conditions? A. Myocardial infarction, muscular dystrophies. (Page 48) Q. What is the advantage of CK estimation over LDH estimation to identify myocardial infarction? (Page 48) A. The CK level starts to rise within three hours of infarction. Therefore, CK estimation is very useful to detect early cases, where ECG changes may be ambiguous. The CK level is not increased in hemolysis or in congestive cardiac failure; and therefore CK has an advantage over LDH. Q. What are the iso-enzymes of CK? (Page 48) A. CK is a dimer, the subunits are called B for brain and M for muscle. Therefore, three iso-enzymes are possible.

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Q. What are the origins of the CK iso-enzymes? (Page 48) A. Eighty percent of molecules in circulation are MM (CK3) variety of skeletal origin, five percent in circulation are MB (CK2) from heart, one percent from brain (BB or CK1) and fifteen percent CKmt from mitochondria. Q. When do you estimate total CK and the iso-enzyme? (Page 48) A. Estimation of total CK is employed in muscular dystrophies and CK-MB iso-enzyme is estimated to identify myocardial infarction. Q. What is the advantage of cardiac troponin I over other parameters to identify the myocardial infarction? (Page 48) A. Cardiac Troponin I is released into the blood within four hours after the onset of cardiac symptoms, peaks at 12-16 hours and remains elevated for 5-9 days post-infarction. Therefore, CTI is very useful as a marker at any time interval after the heart attack. It is 75% sensitive index for myocardial infarction. Q. What is the significance of AST? (Page 48) A. It is significantly elevated in myocardial infarction and moderately elevated in liver diseases. Q. What is the significance of ALT? (Page 49) A. Very high values are seen in acute hepatitis. Rise in ALT levels may be noticed several days before clinical signs such as jaundice are manifested. Moderate increase may be seen in chronic liver diseases such as cirrhosis, and malignancy in liver.

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Q. Alkaline phosphatase level in serum is elevated in which conditions? (Page 49) A. Moderate increase is seen in hepatic diseases (infective hepatitis, alcoholic hepatitis). High levels may be noticed in obstructive jaundice or cholestasis. Very high levels are seen in bone diseases such as Paget’s disease, rickets, osteomalacia, osteoblastoma, metastatic carcinoma of bone. Q. For alkaline phosphatase, how many iso-enzymes are present? (Page 49) A. Six. Q. What is Regan iso-enzyme? (Page 49) A. It is the iso-enzyme of alkaline phosphatase, inhibited by phenylalanine. It is of placental origin. It is elevated in about 15% cases of carcinoma of lung, liver and gut and then named as Regan isoenzyme or carcinoplacental iso-enzyme. Q. It is said that nucleotide phosphatase (NTP) is a better index of obstructive liver disease than alkaline phosphatase (ALP), why? (Page 49) A. ALP level is increased in both liver and bone diseases, but NTP is only in liver diseases. Q. Estimation of gamma glutamyl transferase is useful to detect which condition? (Page 50) A. Alcohol abuse. Q. What are the enzymes useful in diagnosing liver pathology? (Page 50) A. ALT, ALP, GGT, NTP.

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Q. Give the clinical implications of these enzymes. (Page 50) A. In infective hepatitis, ALT level is increased; in alcohol abuse, GGT level is increased; in obstructive jaundice, ALP level is increased. Q. Serum acid phosphatase level is increased in which condition? (Page 50) A. Prostate carcinoma. Q. Total acid phosphatase may increase in some other conditions also; what are they? (Page 50) A. Prostate carcinoma, secondary metastasis in bones, per rectal examination, intravascular hemolysis. Q. In such conditions, iso-enzyme study is helpful or not? (Page 50) A. Yes, tartarate labile iso-enzyme is specific for prostate carcinoma. Q. What is the advantage of prostate specific antigen? (Page 50) A. PSA is very specific for prostate carcinoma. Q. What are the enzymes useful as tumour markers? (Page 50) A. Regan iso-enzyme of ALP for lung tumour; tartarate labile iso-enzyme of ACP and Prostate specific antigen (PSA) for prostate carcinoma; Neuron specific enolase (NSE) for cancers of neuro-endocrine origin.

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Viva—based on Textbook of Biochemistry

Q. Pseudo-cholinesterase deficiency is manifested as what? (Page 50) A. Succinyl choline apnoea; prolonged apnea when succinyl choline is given as anesthetic drug. Q. Which enzyme deficiency is inherited as Xlinked? (Page 50) A. Glucose-6-phosphate-dehydrogenase. Q. How the deficiency of GPD is manifested? (Page 51) A. Drug induced hemolytic anemia. Q. Acute pancreatitis can be diagnosed by estimating which enzymes? (Page 51) A. Amylase and lipase. Q. Name some enzymes that are used as therapeutic agents. (Page 52) A. Asparaginase for leukemia, streptokinase to dissolve clots, and pepsin for indigestion.

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Methods of Separation and Purification of Biological Compounds, Methods of Study of Metabolism Q. What is meant by electrophoresis? (Page 53) A. The term refers to the movement of charged particles through an electrolyte when subjected to an electric field. Q. What are the factors affecting the mobility in electrophoresis? (Page 53) A. Net charge on the particles (pI of proteins), mass and shape of the particles, the pH of the medium, strength of electrical field, and properties of the supporting medium. Q. What are the types of electrophoresis? (Page 53) A. Horizontal and vertical types. Q. What are the supporting media used? (Page 53) A. Filter paper, cellulose acetate, agar gel, agarose gel, starch gel and polyacrylamide gel.

48 Viva—based on Textbook of Biochemistry Q. Electrophoresis is commonly employed for what purpose in laboratory? A. For serum electrophoresis and to see abnormalities in serum protein concentrations. Q. What is the advantage of polyacrylamide gel? (Page 53) A. It has a molecular sieving effect and so separation is very efficient. Q. What is immuno-electrophoresis? (Page 54) A. Here electrophoretic separation is followed by an antigen-antibody reaction. Q. What is the principle of adsorption chromatography? (Page 54) A. separation is based on differences in adsorption at the surface of a solid stationary medium. Q. What is the principle of partition chromatography? (Page 55) A. the components of the mixture to be separated are partitioned between the two phases depending on the partition co-efficient (solubility) of the particular substances. Q. What are the common types of partition chromatography? (Page 55) A. Paper chromatography and thin layer chromatography. Q. What is the advantage of TLC over paper chromatography? (Page 55) A. TLC needs lesser time, and separation is more effective.

Methods of Separation & Purification of Biological Compounds, Methods of Study of Metabolism 49

Q. What is Rf value? (Page 56) A. It is the ratio of the distance travelled by the substance (solute) to the distance travelled by the solvent. The Rf value is a constant for a particular solvent system at a given temperature. Q. What is the basic principle of ion-exchange chromatography? (Page 56) A. Here, the separation is based on electrostatic attraction between charged molecules to oppositely charged groups on the ion exchange resins. Q. What is the principle of gel filtration chromatography? (Page 56) A. The separation is effected on the basis of the size of the molecules. It is otherwise called molecular sieving. Q. Give the principle of affinity chromatography. (Page 56) A. The technique is based on the high affinity of specific proteins for specific chemical groups. Q. Give an example of affinity chromatography. (Page 57) A. Separation and quantitation of glycated hemoglobin. Q. What is the quickest method for separation of proteins? (Page 58) A. HPLC.

50 Viva—based on Textbook of Biochemistry Q. What is the principle of ultracentrifugation? (Page 58) A. Large molecules can be sedimented at high centrifugal forces whereas small molecules cannot. Rate of sedimentation depends on the size, shape and density of solute particles. Q. What is Svedberg unit? (Page 57) A. Sedimentation constant is expressed in Svedberg (S) units. Q. What are the uses of ultracentrifugation? A. 1. Separation of subcellular organelles. 2. Separation of lipoproteins. 3. Determination of molecular weight of proteins. Q. What are the methods used to determine the molecular weight of proteins? A. (1) Ultracentrifugation, (2) Gel filtration and (c) PAGE (poly acrylamide gel electrophoresis). (Page 57) Q. What is the advantage of radio-immuno assay? (Page 57) A. Very small quantities of substances could be accurately measured. Q. What is the radio-active label used for RIA? (Page 58) A. Iodine-125. Q. What is the half life of Iodine-125? A. About 60 days.

(Page 58)

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Q. What are the disadvantages of RIA, when compared to ELISA? (Page 58) A. 1. Since radio-isotopes are used, only approved laboratories could take up the assay. 2. The shelf life of the reagent is short. Q. What are the enzymes commonly used in ELISA technique. (Page 58) A. Alkaline phosphatase (ALP) and horse radish peroxidase (HRP).

52 Viva—based on Textbook of Biochemistry

Carbohydrates-I:

Chemistry, Digestion and Absorption Q. How carbohydrates are classified? (Page 61) A. Based on the number of the sugar units available, they are classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Q. What is a monosaccharide? (Page 61) A. Molecules having only one actual or potential sugar group are called monosaccharides. Q. What is a polysaccharide? (Page 61) A. They contain more than 10 sugar units. Q. How are they combined together? A. Through glycosidic linkages.

(Page 61)

Q. How are monosaccharides further classified? (Page 61) A. Sugars having aldehyde group are called aldoses and sugars with keto group are ketoses.

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Q. Name some important monosaccharides. (Page 61) A. Glucose, fructose, galactose, mannose. Q. What are pentoses? (Page 61) A. Monosaccharides with five carbon atoms. Q. Name a few pentoses. A. Arabinose, Xylose, Ribose.

(Page 61)

Q. Which is the reference carbon atom in sugars? (Page 62) A. Penultimate carbon atom. Q. What is the difference between D and L sugars? (Page 62) A. They are mirror images with reference to penultimate carbon atom. Q. Which isomer is common in nature? (Page 62) A. D variety of sugars are common in nature. Q. Which is the most common monosaccharide in the body? A. Glucose. (Page 62) Q. What is the difference between glucose and galactose? (Page 62) A. They are different with regard to the H and OH groups at the 4th carbon atom. Galactose is the 4th epimer of glucose (Fig.8.3). Q. Galactose is present in which food? (Page 62) A. Lactose is present in milk. Lactose contains galactose and glucose.

54 Viva—based on Textbook of Biochemistry Q. What is epimerism? (Page 62) A. When sugars are different from one another, only in configuration with regard to a single carbon atom (other than the reference carbon atom), they are called epimers. Q. Give an example. (Page 62) A. For example, glucose and mannose are an epimeric pair which differ only with respect to carbon atom 2. Similarly, galactose is the 4th epimer of glucose. (Fig. 8.3). Q. Anomerism is produced with reference with which carbon atom? (Page 62) A. Anomers are produced by the spatial configuration with reference to the first carbon atom in aldoses and second carbon atom in ketoses. (Fig. 8.4). Q. How alpha and beta forms of sugars are produced? (Page 62) A. These are anomers. The difference lies in the spatial configuration with reference to the first carbon atom in aldoses and second carbon atom in ketoses. (Fig. 8.4). Q. What is the basis of mutarotation? (Page 62) A. It is due to the anomeric carbon atom. Q. What is the difference between glucose and fructose? A. Glucose is an aldohexose, and fructose is a ketohexose.

Carbohydrates-I

Q. Name a ketose. A. Fructose.

55

(Page 63)

Q. What is the principle of Benedict’s test? (Page 64) A. In alkaline medium, sugar will cause reduction of cupric ions, to form red coloured precipitate. Q. What is the composition of Benedict’s reagent. (Page 64) A. It contains sodium carbonate, copper sulfate and sodium citrate. In the alkaline medium provided by sodium carbonate, the copper remains as cupric hydroxide. Sodium citrate acts as a stabilising agent to prevent precipitation of cupric hydroxide. Q. Benedict’s test is commonly employed for what? (Page 64) A. To detect the presence of glucose in urine. Q. Name a few reducing sugars. A. Glucose, fructose, mannose.

(Page 64)

Q. Keto group is non-reducing, but fructose reduces Benedict’s solution, what is the cause for this anomaly? (Fig. 8.10) A. In alkaline medium, ketone group is converted to aldehyde, through enediol formation. Q. In the case of sugars, which of the properties go hand in hand? A. Reducing property, osazone formation and mutarotation. (page 64)

56 Viva—based on Textbook of Biochemistry Q. Glucose and fructose will form identical osazones, why? A. The difference in glucose and fructose is dependent on the first and second carbon atoms, and this is masked by the osazone formation. (Page 64) Q. On oxidation of glucose, what are produced? (Page 64) A. Glucuronic acid, gluconic acid and glucosaccharic acid. Q. Reduction of glucose produces what? (Page 64) A. Sorbitol. Q. Name some deoxy sugars. (Page 66) A. Deoxy ribose, fucose (deoxy galactose). Q. Which is the stain used to identify deoxysugar? (Page 66) A. Feulgen staining. Q. Name some important disaccharides. (Page 67) A. Sucrose, lactose, maltose. Q. What is the glycosidic linkage in lactose? (Page 67) A. Beta 1-4 linkage. Q. What is the glycosidic linkage in sucrose? (Page 67) A. 1-2 linkage.

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Q. Which disaccharide has no free aldehyde or ketone group? A. Sucrose. (Page 67) Q. Glucose and fructose are reducing sugars, but sucrose (containing glucose and fructose) is a non-reducing sugar, why? (Page 67) A. Because the glycosidic linkage in sucrose involves 1st carbon of glucose and 2nd carbon of fructose, so both reducing groups are masked. Q. Hydrolysis of maltose will give rise to what ? (Page 67) A. Two glucose units. Q. Which is the sugar found in milk? A. Lactose.

(Page 67)

Q. What are the component monosaccharides of lactose? (Page 67) A. Galactose and glucose. Q. Sucrose consists of what monosaccharides? (Page 67) A. Glucose + fructose. Q. Name reducing disaccharides. A. Lactose and maltose.

(Page 67)

Q. How polysaccharides are classified? (Page 68) A. Homopolysaccharides (homoglycans) and heteropolysaccharides (heteroglycans). Q. What is a homopolysaccharide? (Page 68) A. They are composed of single kind of monosaccharides.

58 Viva—based on Textbook of Biochemistry Q. Give examples of homopolysaccharides. (Page 68) A. Starch, and glycogen. Q. What are heteropolysaccharides? (Page 68) A. They are composed of two or more different monosaccharides. Q. What are the characteristics of glycogen? (Page 69) A. It is composed of glucose units. It is the stored form of carbohydrate in animal kingdom. It has a highly branched structure. Q. What is the reserve carbohydrate in plant kingdom? (Page 69) A. Starch. Q. What is the end product of action of pancreatic amylase on starch? (Page 69) A. Maltose. Q. Cellulose and starch are polysaccharides made of glucose, but cellulose cannot be digest by human beings, why? (Page 69) A. Cellulose contains beta 1,4 linkages, which cannot be digested by human enzymes. Q. What is inulin? (Page 69) A. It is a homopolysaccharide, composed of fructose units. Q. What is the use of inulin? (Page 69) A. It is used to find renal clearance and glomerular filtration rate.

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Q. Give examples of heteropolysaccharides. (Page 70) A. Agar, hyaluronic acid, heparin, chondroitin sulfate. Q. What are mucopolysaccharides? (Page 70) A. They contain uronic acid and amino sugars. Q. Which heteropolysaccharide does not contain uronic acid? (Page 70) A. Keratan sulfate. Q. Hyaluronic acid is seen in which tissues? (Page 70) A. Connective tissue, synovial fluid, tendons, vitreous humor. Q. What is the difference between glycoprotein and mucoprotein? (Page 71) A. If the carbohydrate content is less than 10%, it is called a glycoprotein. If the carbohydrate content is more than 10% it is a mucoprotein. Q. The rate of absorption of sugars in intestine is highest for which monosaccharide? (Page 71) A. Absorption rate of galactose is more than glucose, while fructose is absorbed at a lesser rate than glucose. Q. Glucose is absorbed at the luminal side of gastro intestinal cells by which mechanism? (Page 72, and Fig. 8.30) A. Carrier mediated co-transport with sodium, named as sodium dependent glucose transporter (SGluT).

60 Viva—based on Textbook of Biochemistry Q. How glucose is released from intestinal cells into the blood stream? A. Glucose transporter type 2 (GluT2) (Fig.8.30). Q. How glucose is taken up by cells from blood stream? (Page 72) A. In tissues GluT2 is involved in absorption of glucose from blood. Q. What is the importance of GluT4? (Page 72) A. It is the glucose transporter present in muscle and adipose tissues. Insulin induces these transporters. In diabetes mellitus, entry of glucose into muscle is decreased, because GluT4 is reduced in insulin deficiency. Q. What is the glucose sensor in the beta cells of pancreas? (Page 72) A. GluT2 acts as the glucose sensor mechanism, for the controlled supply of insulin into blood stream.

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Carbohydrates-II:

Major Metabolic Pathways of Glucose, Glycolysis, Gluconeogenesis, Glycogen Metabolism Q. What is glycolysis? (Page 73) A. In this pathway, glucose is converted to pyruvate or lactate, along with production of a small quantity of energy. Q. In which condition pyruvate is produced, and when lactate? (Page 73) A. In aerobic condition pyruvate is produced. When oxygen is lacking, lactate is produced. Q. What is the significance of Glycolysis?(Page 73) A. It is the only pathway that is taking place in all the cells of the body. Glycolysis is the only source of energy in erythrocytes. Moreover, anaerobic glycolysis forms the major source of energy in actively contracting muscles.

62 Viva—based on Textbook of Biochemistry Q. What is hexokinase? (Page 73) A. Hexokinase is the first step in the glycolysis pathway. It phosphorylates glucose to glucose-6-phosphate. Q. What is glucokinase? (Page 73) A. The reaction is similar to hexokinase. But glucokinase is present only in liver, acts specifically on glucose, and is active when glucose level in blood is increased after a food. Q. Which tissues prefer anaerobic glycolysis? (Page 73) A. RBCs, exercising muscle, and cancer cells. Q. What is the importance of phospho fructokinase? (Page 74) A. It is the key enzyme (rate limiting enzyme) of the pathway. It is an irreversible reaction. Q. What is the substrate for aldolase reaction? (Page 74) A. Fructose-1,6-bisphosphate. Q. During glycolysis, energy is produced during which steps? (Page 74, 75) A. Step 5, glyceraldehyde-3-phosphate to 1,3bisphospho glycerate, Step 6, 1,3-bis phospho glycerate to 3-phospho glycerate, and Step 9, Phospho enol pyruvate to pyruvate. Q. Fluoride ions inhibit which enzyme? (Page 75) A. Enolase.

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Q. What is the importance of the above inhibition? (Page 75) A. Fluoride is used to prevent glycolysis, as preservative for blood before glucose estimation. Q. NAD is reduced to NADH in which reaction of glycolysis? (Page 75) A. Glyceraldehyde-3-phosphate dehydrogenase reaction. Q. NADH is oxidised to NAD in which reaction of glycolysis? (Page 76) A. Lactate dehydrogenase reaction. Q. What are substrate level phosphorylations in glycolysis? (Page 75, 76) A. 1,3-bisphospho glycerate kinase (step 6) and pyruvate kinase (step 9). Q. What is the purpose of lactic acid production under anaerobic conditions? A. NADH generated in the 5th step has to be oxidised to NAD+. This can be done by oxygen. But when oxygen is lacking, the 5th step has to be coupled with the 10th step for regeneration of NAD. (See Fig. 9.11) Q. As the end product of glycolysis, pyruvate and NADH are formed. During anaerobiasis, this NADH is reconverted to NAD+ by what mechanism? (Page 76) A. Lactate dehydrogenase reaction.

64 Viva—based on Textbook of Biochemistry Q. As the end product of glycolysis, pyruvate and NADH are formed. During aerobic conditions, this NADH is reconverted to NAD+ by what mechanism? (Page 76) A. Oxygen. Q. What is Cori’s cycle? (Fig.9.13) A. During exercise, lactate is produced in muscle. This lactate diffuses into the blood. Lactate then reaches liver, where it is oxidised to pyruvate. It is then taken up through gluconeogenesis pathway, and becomes glucose. This glucose can enter into blood and then taken to muscle. This cycle is called Cori’s cycle, or lactic acid cycle. Q. What is the purpose of Cori’s cycle? (Page 77) A. By this means, the lactate is efficiently reutilised by the body. Q. Why lactate is transported from muscle to liver? (Page 77) A. Oxygen is limited in muscle, so lactic acid could not be made to pyruvate in muscle. So, it is transported to liver, where it is made to pyruvate and then to glucose. Q. What are the inhibitors of phosphofructokinase? (Page 77) A. ATP, Citrate, Glucocorticoids. Q. What are the activators of phospho fructo kinase? (Page 77, 78) A. AMP, Fructose-2,6-bisphosphate, Fructose-6phosphate.

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Q. What are key glycolytic enzymes? (Page 77, 78) A. Glucokinase, Phospho fructo kinase, Pyruvate kinase. Q. What is the action of insulin on glycolysis? (Page 77, 78) A. Insulin stimulates glycolysis. Q. What is the net yield of ATP from one glucose molecule during anaerobic glycolysis? (Page 78 and Table 9.3) A. 2 ATP. Q. In aerobic glycolysis, the net yield from one glucose molecule is how much? (Page 78 and Table 9.4) A. 8 ATP. Q. During complete oxidation, what is the net yield of ATP from one glucose molecule? (Page 78 and Table 9.5) A. 38 ATP. Q. How many ATPs are generated per one rotation of the citric acid cycle? A. 12 ATP. Q. What is the function of 2,3-bisphospho glycerate? (Page 79) A. When combined with hemoglobin, 2,3-BPG reduces the affinity towards oxygen. Q. What are the steps in which carbon dioxide is produced from a glucose molecule? (Page 80) A. Pyruvate dehydrogenase, isocitrate dehydrogenase, alpha keto glutarate dehydrogenase.

66 Viva—based on Textbook of Biochemistry Q. What are the co-enzymes necessary for oxidative decarboxylation of pyruvate? (Page 80) A. Thiamine pyrophosphate, NAD, FAD, Lipoic acid, Co-enzyme A. Q. What is pyruvate dehydrogenase? (Fig. 9.19) A. The enzyme catalysing the reaction, pyruvate to acetyl CoA. Q. What is pyruvate carboxylase? (Fig. 9.20) A. The enzyme catalysing the reaction, pyruvate to oxaloacetate. Q. What is pyruvate kinase? (Fig. 9.20) A. It catalyses the reaction, phospho enol pyruvate to pyruvate. Q. There is no net synthesis of glucose from fatty acids, why? (Page 80) A. Pyruvate to acetyl CoA is a totally irreversible reaction. Q. Which enzyme irreversibly channels glucose to energy production, rather than retaining glucose for blood sugar regulation? (Page 80) A. Pyruvate dehydrogenase is an irreversible reaction. Q. Pyruvate is converted to acetyl CoA by which enzyme? (Page 80) A. Pyruvate dehydrogenate. Q. What is gluconeogenesis? (Page 81) A. Production of glucose from non-carbohydrate sources.

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Q. What are those non-carbohydrate sources? (What are the substrates for gluconeogenesis?). (Page 82, 83) A. Glucogenic amino acids and lactate. Q. What are the key gluconeogenic enzymes? (Page 82) A. Pyruvate carboxylase, Phospho enol pyruvate carboxy kinase, Fructose-1,6-bisphosphatase and Glucose-6-phosphatase. Q. Pyruvate carboxylase reaction (pyruvate to oxaloacetate) needs which co-enzyme? (Page 81) A. Biotin and ATP. Q. Malate shuttle is used for what purpose? (Page 82) A. Reactions of gluconeogenesis are taking place in cytosol. Hence the oxaloacetate has to be transported from mitochondria to cytosol. This is achieved by the malate shuttle (see Fig. 9.22). Q. Gluconeogenesis is taking place in which tissue? (Page 81) A. Liver. Q. How many ATP molecules are required to convert two molecules of pyruvate into glucose? (Page 82) A. Six. Q. Blood glucose level can be raised by gluconeogenesis only by liver, why? (Page 82) A. Glucose-6-phosphatase is present only in liver.

68 Viva—based on Textbook of Biochemistry Q. Muscle glycogen will not serve as a precursor of blood sugar, why? (Page 82) A. Glucose-6-phosphatase is absent in muscle. Q. Which amino acids are both ketogenic and glucogenic? (Fig. 9.29) A. Tyrosine and tryptophan. Q. What will inhibit gluconeogenesis? A. Insulin.

(Page 85)

Q. What will stimulate gluconeogenesis? (Page 85) A. Glucagon and glucocorticoids. Q. What is the significance of gluconeogenesis? (Page 85) A. Gluconeogenesis is necessary to maintain blood glucose level especially under conditions of starvation. Q. What is glycogenolysis? A. Degradation of glycogen to glucose.

(Page 86)

Q. What is the main enzyme for glycogenolysis? (Page 86) A. Glycogen phosphorylase. Q. Which hormones enhance glycogenolysis? (Page 87) A. Adrenaline and glucagon causes glycogenolysis. Q. What is the mechanism of action of adrenaline? (Page 87) A. Adrenaline increases cyclic AMP level which activates glycogen phosphorylase.

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Q. In the glycogen synthesis, which is the active glucose derivative? A. UDP-glucose. Q. Adrenaline acts on which enzyme? A. Glycogen phosphorylase. Q. What will activate glycogen phosphorylase? (Page 87) A. Epinephrine, glucagon, cyclic AMP. Q. Which is the defective enzyme in von Gierke’s disease (glycogen storage disease type I)? (Page 89) A. Glucose-6-phosphatase. Q. What are the characteristic clinical features of von Gierke’s disease? A. Fasting hypoglycemia, which does not respond to adrenaline is very characteristic. (Page 89)

70 Viva—based on Textbook of Biochemistry

Carbohydrates-III:

Regulation of Blood Sugar, Insulin and Diabets Mellitus Q. What is the level of fasting blood sugar in a normal person? A. 70-110 mg/dl. (Page 90) Q. Which hormone is hypoglycemic? A. Insulin.

(Page 90)

Q. What are the major actions of insulin? (Page 90) A. Insulin decreases blood sugar, it stimulates glycolysis, inhibits gluconeogenesis, enhances glycogen synthesis and inhibits lipolysis. Q. What are the anti-insulin (hyperglycemic) hormones? (Page 90) A. Glucagon, adrenaline, corticosteroids, growth hormone. Q. What are the major actions of glucagon? (Page 91) A. Promotes glycogenolysis, enhances gluconeogenesis, depresses glycogen synthesis, inhibits glycolysis.

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Q. What is the best method for glucose estimation? (Page 91) A. Glucose oxidase peroxidase (GOD-POD) method. Q. What is the major indication for doing an oral glucose tolerance test (OGTT)? (Page 92) A. Patient has symptoms suggestive of diabetes mellitus, but fasting blood sugar value is inconclusive (between 100 and 126 mg/dl). Q. What are the precautions to take before OGTT? (Page 92) A. Patient should have a good carbohydrate diet for three days prior to the test. Patient should avoid insulin and oral antidiabetic drugs. Patient should fast overnight. Patient should not take any breakfast. Q. What is the glucose load dose? (Page 92) A. Seventy five gram anhydrous glucose (82.5 g of glucose monohydrate) in 250-300 ml of water. Q. What precaution would you take in giving the glucose load? (Page 92) A. In order to prevent vomiting, patient is asked to drink it slowly (within about 5 minutes). Flavouring of the solution will also reduce the tendency to vomit. Q. What are the criteria for diagnosing diabetic mellitus? (Table 10.1). (Page 92) A. Fasting plasma sugar is more than 126 mg/dl, on more than one occasion. 2. Or, if 2-hour post-glucose load value of OGTT is more than 200 mg/dl (even at one occasion). 3. Or, if both fasting and 2hour values are above these levels, on the same occasion.

72 Viva—based on Textbook of Biochemistry Q. Can you diagnose diabetes on the basis of random blood estimations? (Page 92) A. Diabetes is diagnosed, if the random plasma sugar level is more than 200 mg/dl, on more than one occasion. Diagnosis should not be based on a single random test alone, it should be repeated. Q. When a standard oral glucose tolerance test was done, the blood glucose levels of the patient were found as:0 min = 130 mg/dl and 120 min = 220 mg /dl. What will be your diagnosis? (Page 92) A. Diabetes mellitus. Q. What is impaired glucose tolerance (IGT)? (Page 93) A. When fasting plasma glucose level is between 110 and 126 mg/dl and 2-hour post-glucose value is between 140 and 200 mg/dl. Q. When a standard oral glucose tolerance test was done, the blood glucose levels of the patient were found as:0 min = 120 mg/dl, 120 min = 160 mg / dl. What is your diagnosis? A. Impaired glucose tolerance. (Page 93) Q. What you will do for such persons? (Page 93) A. Such persons need careful follow up because IGT progresses to frank diabetes at the rate of 2% patients per year. Q. What is impaired fasting glycemia (IFG). (Page 93) A. In this condition, fasting plasma sugar is abnormal (between 110 and 126 mg/dl), but the 2-hour post-glucose value is within normal limits (less than 140 mg/dl).

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Q. What you will do for such persons? (Page 93) A. These persons need no immediate treatment, but are to be kept under constant check-up. They are at increased risk for development of diabetes or cardiovascular diseases. Q. What is gestational diabetes mellitus (GDM)? (Page 93) A. This term is used when carbohydrate intolerance is noticed, for the first time, during a pregnancy. If the fasting value is more than 126 mg%, it is taken as gestational diabetes. Q. If a known diabetic patient, who becomes pregnant, will you include her in the category of GDM? (Page 93) A. No. Q. What is the clinical significance of GDM? (Page 93) A. Women with GDM are at increased risk for subsequent development of frank diabetes. GDM is associated with increased birth weight of child and increased incidence of neonatal mortality. Q. After delivery, what you will do for a person with GDM? (Page 93) A. After the child birth, the women should be re assessed and accordingly classified as having either diabetes mellitus or normal glucose tolerance, based on the results of a fresh OGTT. Q. What are other conditions which may cause impaired glucose tolerance? (Page 93) A. Alimentary glucosuria, renal glucosuria.

74 Viva—based on Textbook of Biochemistry Q. What is renal glucosuria? (Page 93) A. Here glucose is excreted in urine due to a lowering of renal threshold. The blood sugar levels are within normal limits. Q. What is normal renal threshold for glucose? (Page 93) A. 180 mg/100 ml. Q. What are the reducing substances seen in urine? (Page 94) A. Glucose, fructose, lactose, galactose, pentoses, ascorbic acid, glucuronides. Q. What is transient glucosuria? (Page 94) A. It may occur in some people due to emotional stress. Excessive secretion of catecholamines will produce hyperglycemia and resultant glucosuria. Once theÿstress is removed, the glucosuria disappears. Q. What is fructosuria? (Page 94) A. Presence of fructose in urine. It is due to the deficiency of fructokinase or aldolase B (Fig.11.11). Q. What is lactosuria? (Page 94) A. It is observed in the urine of normal women during 3rd trimester of pregnancy and during lactation. Q. What is the clinical importance of lactosuria? (Page 94) A. The condition is harmless. But it is important to distinguish lactosuria from glucosuria when gestational diabetes mellitus is suspected.

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Q. What is the test for reducing sugars in urine? (Page 95) A. Benedict’s test. Q. What are the pathways stimulated by insulin? (Page 96) A. Glycolysis, glycogen synthesis, HMP shunt pathway, lipogenesis. Q. Name important enzymes that are stimulated by Insulin. (Page 96) A. Phospho fructo kinase, glycogen synthase, glucose-6-phosphate dehydrogenase, acetyl CoA carboxylase. Q. What are the pathways inhibited by insulin? (Page 96) A. Gluconeogenesis, glycogenolysis, lipolysis, ketogenesis. Q. What are the important enzymes inhibited by insulin? (Page 96) A. Glucose-6-phosphatase, glycogen phosphorylase, hormone sensitive lipase. Q. Where is insulin synthesised? A. Beta cells of langerhans of pancreas.

(Page 96)

Q. What is proinsulin? (Page 96) A. Insulin is synthesised as a large single polypeptide. Middle part of it is then removed, to form the A and B chains of insulin. Q. What is C peptide? (Page 96) A. It is the part removed from proinsulin during the maturation of insulin molecule.

76 Viva—based on Textbook of Biochemistry Q. What is the clinical significance of C peptide? (Page 96) A. Sometimes measurement of endogenous insulin may be difficult because of the presence of antibodies against insulin in the circulation. Then measurement of C-peptide is useful. Q. What are the salient structural features of insulin? (Page 96) A. Insulin is a protein hormone with two poly peptide chains, the A chain with 21 amino acids and the B chain with 30 amino acids are joined together by a pair of disulfide bonds. It has a total of 51 amino acids. Q. How is insulin secretion controlled? (Page 96) A. Glucose is the major stimulant of insulin secretion. Q. How glucose stimulates insulin secretion? (Page 96) A. The beta cells have GluT 2 receptors, these act as sensor mechanism for glucose level. The insulin secretion is controlled by a cyclic AMP-mediated mechanism. Cyclic AMP along with calcium causes the insulin secretion. Q. What is the effect of insulin on glucose uptake of cells? (Page 97) A. Insulin facilitates the membrane transport of glucose in most of tissues, especially in muscles and adipose tissue. This is by glucose transporter, GIuT4. But glucose uptake by GlT2 is independent of insulin, it is seen in liver and brain.

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Q. Maximum glucose utilisation is seen in which tissue? (Page 97) A. At basal rates, brain utilises 60% of sugar oxidised. Q. What is the mechanism of action of insulin? (Page 97) A. Insulin acts by binding to membrane receptor, on the target cells. Q. What is the structural feature of insulin receptor? (Page 97) A. Insulin receptor has four subunits, two alpha and two beta subunits. The alpha units are located on the extracellular side, to which insulin binds. The beta subunits are towards cytoplasmic side. Beta subunit has tyrosine kinase activity. Q. How diabetes mellitus is classified? A. Type 1 and type 2.

(Page 99)

Q. What are the characteristic features of type 1, diabetes mellitus? A. Here circulating insulin level is deficient. These patients are dependent on insulin injections. Onset is during adolescence. Rapid loss of body weight is observed. They are more prone to developing ketosis. Q. What about type 2 diabetes mellitus? (Page 100) A. Most of the patients belong to this type. Here circulating insulin level is normal, but there is a relative insulin deficiency. It is commonly seen in individuals above 40 years. These patients are less prone to developing ketosis.

78 Viva—based on Textbook of Biochemistry Q. What is maturity onset diabetes of young (MODY)? (Page 100) A. It is due to defective glucokinase. Q. What are the cardinal symptoms of diabetes mellitus? (Page 100) A. Polyuria, polydypsia, polyphagia and weight loss. Q. What is the reason for polyuria in diabetes mellitus? (Page 100) A. When the blood glucose level exceeds the renal threshold glucose is excreted in urine. Due to osmotic effect, more water accompanies the glucose. Q. What is the reason for polydypsia in diabetes mellitus? (Page 100) A. To compensate for this loss of water, thirst centre is activated, and more water is taken (polydypsia). Q. What is the reason for weight loss in diabetes mellitus? (Page 100) A. The loss and ineffective utilisation of glucose leads to breakdown of fat and protein.ÿThis would lead to loss of weight. Q. What is the reason for polyphagia in diabetes mellitus? (Page 100) A. To compensate the loss of glucose and protein, patient takes more food. Q. What are the acute complications of diabetes mellitus? (Page 100) A. Keto acidosis, hyperosmolar non-ketotic coma, lactic acidosis.

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Q. What are the chronic complications of diabetes mellitus? (Page 101) A. Thrombosis, paralysis, gangrene, micro-angiopathy, nephrosclerosis, cataract, peripheral neuropathy. Q. What is micro-albuminuria? (Page 101) A. Albumin 50 to 300 mg/day in urine. It is a predictor of progressive renal damage, atherosclerotic diseases and cardiovascular mortality. Albumin more than 300 mg/day indicates overt diabetic nephropathy. Q. What is the cause for cataract in diabetes mellitus? (Page 101) A. Early development of cataract of lens is due to the increased rate of sorbitol formation, caused by the hyperglycemia. Q. What is the difference between glycosylation and glycation? A. Enzymatic addition of any sugar to a protein is called “glycosylation” while non-enzymatic process is termed “glycation”. (Page 101) Q. What is the basis of glycation? (Page 101) A. When there is hyperglycemia, proteins in the body may undergo glycation. It is a non-enzymatic process. Glucose is added to the N-terminal amino group of proteins.

80 Viva—based on Textbook of Biochemistry Q. What is the significance of glycated hemoglobin? (Page 101) A. The determination of glycated hemoglobin is not for diagnosis of diabetes mellitus, but for monitoring the response of treatment. It is unaffected by recent food intake or recent changes in blood sugar levels. An elevated glycohemoglobin indicates poor control of diabetes mellitus. The risk of retinopathy and renal complications are proportionately increased with elevated glycatedhemoglobin.

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Carbohydrates-IV:

Other Metabolic Pathways (HMP Shunt Pathway, Fructose, Galactose, Glucuronic Acid, Alcohol) Q. HMP shunt pathway use how much glucose? (Page 103) A. About 10% of glucose molecules per day are entering in this pathway. Q. What are the tissues in which HMP shunt pathway is significant? (Page 103) A. Liver, adipose tissue, RBC, adrenal cortex, ovary, testis, mammary gland, lens. Q. Which is the key enzyme of hexose monophosphate shunt pathway? (Page 103) A. Glucose-6-phosphate dehydrogenase. Q. What is the hormonal control over HMP shunt pathway? (Page 103) A. Insulin stimulates the pathway by activating the key enzyme.

82 Viva—based on Textbook of Biochemistry Q. Which enzyme generates NADPH? (Page 103) A. Glucose-6-phosphate dehydrogenase. Q. What is the purpose of HMP shunt pathway? (Page 104) A. It generates NADPH. Q. What is the use of NADPH in biological systems? (Page 105) A. For reductive biosynthesis. Q. What reductive biosynthesis pathways need NADPH? (Page 105) A. Fatty acid biosynthesis, synthesis of cholesterol, steroid hormones. Q. Apart from reductive synthesis, NADPH is used for what purpose? (Page 105) A. It is necessary to keep the integrity of RBC membrane, it is needed for keeping glutathione in reduced state, it is required for keeping transparency of lens, it is necessary for superoxide production inside macrophages. Q. What about ATP generation? NADPH is used for that? (Page 106) A. No. NADPH is not used for ATP generation. Q. Apart from NADPH generation, is there any other purpose for the HMPshunt pathway? (Page 106) A. The pathway is required for the synthesis of ribose, the pentose phosphates are necessary for nucleotide (DNA and RNA) synthesis.

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Q. What is the manifestation of glucose-6-phosphate dehydrogenase deficiency? (Page 106) A. Drug induced hemolysis and met-hemoglobinemia. Q. Acute hemolytic episode after administration of antimalarial drug is due to what? (Page 106) A. Deficiency of glucose-6-phosphate dehydrogenase. Q. What is the most common enzyme deficiency in man? (Page 106) A. Glucose-6-phosphate dehydrogenase deficiency. Q. What is the mode of hereditary transmission of GPD deficiency? (Page 106) A. It is transmitted as an x-linked recessive character. Q. Is there any advantage of the abnormal gene? (Page 106) A. The geographical distribution of GPD deficiency correlates well with the malarial endemicity. The GPD deficiency offers resistance to malarial infection. Q. What is the clinical significance of transketolase enzyme? (Page 107) A. The transketolase reaction is measured in RBCs as an index of the thiamine status of an individual. Q. Abnormal transketolase leads to what clinical condition? (Page 107) A. The occurrence of Wernick’s encephalopathy (seen in alcoholics and in thiamine deficiency) is due to a genetic defect in the enzyme transketolase. It occurs owing to the enzyme having low binding capacity for TPP.

84 Viva—based on Textbook of Biochemistry Q. Transketolase activity is decreased in the deficiency what? (Page 107) A. Thiamine pyrophosphate (TPP). Q. What is the purpose of uronic acid pathway? (Page 107) A. It is used for conjugation of bilirubin, steroids, synthesis of gluco-saminoglycans. Q. In lower animals, uronic acid pathway is used for what purpose? (Page 107) A. For synthesis of ascorbic acid (vitamin C). Q. What is essential pentosuria? (Page 107) A. Excretion of pentose (L-xylulose) in urine due to the deficiency of xylitol dehydrogenase. Q. What is its importance? (Page 107) A. It does not produce any harm. But it gives a positive reaction to Benedict’s test, so it should be differentiated from diabetes mellitus. Q. What is the clinical significance of polyol pathway? (Page 107) A. The elevated level of sorbitol has been implicated in the development of neuropathy, cataract and retinopathy in diabetes mellitus. Q. Fructokinase catalyses which reaction? (Page 108) A. Fructose to fructose-1-phosphate. Q. What is fructose intolerance? (Page 108) A. Due defective aldolase-B, fructose-1-phosphate accumulates. This leads to accumulation of glycogen in liver, and hypoglycemia.

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Q. Free fructose is seen in which body fluid? (Page 108) A. Seminal plasma. Q. This fructose is produced by which pathway? (Page 107) A. Polyol pathway of glucose. Q. What is the clinical application of fructose estimation in semen? (Page 108) A. Fructose is secreted by seminal vesicles. A block in seminal vessels is indicated by the absence of fructose in semen. Q. What is fructosuria? (Page 108) A. It is a benign metabolic defect due to deficiency of fructokinase. Urine gives positive Benedict’s test, and so it should be differentiated from diabetes mellitus. Q. Neonatal hypoglycemia is seen in which conditions? (Page 109) A. Glycogen storage disease, type I, galactosemia, fructose intolerance. Q. What are the features of galactosemia? (Page 109) A. Congenital cataract, mental retardation, neonatal hypoglycemia, hepatosplenomegaly, positive Benedict’s test. Q. Congenital cataract is seen in which condition? (Page 109) A. Galactosemia.

86 Viva—based on Textbook of Biochemistry Q. Galactosemia is due the absence of which enzyme? (Page 109) A. Galactose-1-phosphate uridyl transferase. Q. What is the treatment policy in galactosemia? (Page 110) A. Lactose free diet is given for first five years of life. Q. Why five years, why life-long treatment is not required? (Page 110) A. By five years, the alternate pathway (galatose-1phosphate pyrophosphorylase) becomes active. Q. Why excessive intake of alcohol produces lactic acidosis? (Page 110) A. During alcohol oxidation, NADH is generated, which converts pyruvate to lactate. Q. Why excessive intake of alcohol produces hypoglycemia? (Page 110) A. Because ethanol inhibits gluconeogenesis. Q. What are the results of chronic alcoholism? (Page 111) A. Polyneuropathy, fatty liver, cirrhosis, Werneck’s encephalopathy. Q. How N-acetyl neuraminic acid (sialic acid) is synthesised? (Page 111) A. N-acetyl mannosamine-6-phosphate + phospho enol pyruvate.

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Q. In glycoproteins, carbohydrate residues are attached to which group of the polypeptide chain? (Page 112) A. Hydroxyl group of serine or threonine. Q. Increased glucosaminoglycans in urine is seen in which condition? (Page 113) A. Mucopolysaccharidosis.

88 Viva—based on Textbook of Biochemistry

Lipids-I:

Chemistry, Digestion and Absorption of Lipids

Q. How lipids are classified? A. Simple, compound and derived.

(Page 115)

Q. Classify fatty acids. (Page 115) A. Depending on the total number of carbon atoms, they are classified as even chain and odd chain. Q. Which type is prevalent in human body? (Page 115) A. Even chain fatty acids. Q. Fatty acids are classified in any other manner? (Page 116) A. They are also classified as saturated or unsaturated fatty acids. Q. What fatty acids are generally present in human fat? (Page 116) A. Mainly Oleic acid, then comes palmitic acid and linoleic acid.

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Q. How many carbon atoms are present in oleic acid? (Page 116) A. 18 carbon, with one double bond. Q. Name some unsaturated fatty acids. (Page 117) A. Oleic, linoleic, linolenic and arachidonic acids. Q. Name some polyunsaturated fatty acids. (Page 117) A. Linoleic, linolenic and arachidonic acids. Q. What is the structure of linoleic acid?

(Page 117)

A. 18 carbon, with two double bonds. Q. What is the structure of linolenic acid? (Page 117) A. 18 carbon with three double bonds. Q. What is the structure of arachidonic acid? (Page 117) A. 20 carbon with four double bonds. Q. Which contains good quantity of PUFA? (Page 118) A. Vegetable oils such as sunflower oil, ground nut oil. Q. Which contains very low level of PUFA? (Page 118) A. Coconut oil and animal fats.

90 Viva—based on Textbook of Biochemistry Q. What is the advantage of storing energy as triglycerides in the body? (Page 119) A. Space requirement is less, storage does not require water, can be mobilised whenever required, capacity for storage is unlimited. Q. What is saponification? (Page 119) A. Hydrolysis of fat by alkali is called are saponification. Q. Does saponification number of a fat molecule increase or decrease with the molecular weight of the fat? (Page 119) A. Decreases with increase in molecular weight of fat. Q. Odour of rancid oil is due to what? (Page 119) A. Partial oxidation of fatty acids, with formation of epoxides and peroxides of small molecular weight fatty acids. Q. Complete digestion of triacyl glycerol (triglyceride) in gastro intestinal tract needs what enzymes? (Page 120) A. Pancreatic lipase, co-lipase, isomerase and bile salts Q. What is the function of pancreatic lipase? (Page 120) A. Partial hydrolysis of triacyl glycerol. The products are 2-mono acylglycerol (2-MAG) (?-monoglyceride) and two fatty acid molecule (Fig. 12.7).

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Q. What is the function of isomerase? (Page 120) A. Isomerase shifts the ester bond from position 2 to 1, this is then hydrolysed by the lipase to form free glycerol and fatty acid. Q. Will there be complete breakdown of triglyceride into fatty acid in the gastro intestinal tract? (Page 120) A. No, only partial digestion is possible. Q. What are the final end products of digestion of triglyceride? (Page 120) A. 2-monoacyl glyceride (78%), 1-monoacyl glyceride (6%), glycerol and fatty acids (14%). Q. How small chain fatty acids are absorbed? (Page 120) A. Small chain and medium chain fatty acids (chain length less than 14 carbons) are directly absorbed from the intestinal lumen into the portal vein and taken to the liver. Q. How long chain fatty acids are absorbed? (Page 120) A. Long chain fatty acids (chain length more than 14 carbons) are absorbed by forming micelles with the help of bile salts. Q. How bile salts help in the absorption of dietary lipids? (Page 120) A. By emulsifying the lipids and producing micelles of lipids. Q. What is the chemical name of bile salts? (Page 120) A. Sodium glycocholate and sodium taurocholate.

92 Viva—based on Textbook of Biochemistry Q. What are micelles? (Page 120) A. The micelles are spherical particles with a hydrophilic exterior and hydrophobic interior core (Fig. 12.8). Monoglycerides, long chain fatty acids, cholesterol, phospholipids and lysophospholipids are incorporated into molecular aggregates to form mixed micelles. Q. What happens to the micelles? (Page 120) A. Fatty acids and monoacyl glycerides from the micelles passively diffuse into the mucosal cell. Q. What happens to the fatty acids in the mucosal cell? (Page 120) A. Once inside the intestinal mucosal cell, the long chain fatty acids are re-esterified to form triglycerides (Fig.12.9). Q. What is the further fate of this triglyceride? (Page 121) A. The triglyceride, along with phospholipids, apoproteins B48, and apo-A are incorporated into chylomicrons. The chyle (milky fluid) from the intestinal mucosal cells loaded with chylomicrons are transported through the lacteals into the thoracic duct and then emptied into systemic circulation. Q. What is the difference for absorption of short chain fatty acid? (Page 120) A. Short and medium chain fatty acids do not need re-esterification. They directly enter into blood vessels (Not to lacteals).

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Q. Where will you find short and medium chain fatty acids? (Page 120) A. They are seen in butter, ghee, coconut oil and mother’s milk. Q. What happens to the bile salts of micelle? (Page 120) A. The bile salts are left behind. Q. What is enterohepatic circulation of bile salts? (Page 120) A. They are separately reabsorbed from the ileum and returned to the liver to be re-excreted again to gut. Q. What is steatorrhea? (Page 121) A. When excretion of fat in faeces is more than 6 g per day, it is called steatorrhea. Q. What is it due to? (Page 121) A. It is due to defective digestion as in chronic diseases of pancreas. In such cases, unsplit fat is excreted in feces. Q. What happens in defective absorption? (Page 121) A. If the absorption alone is defective, most of the fat in faeces may be split fat, i.e. fatty acids and monoglycerides. Q. What is the cause for defective absorption of fat? (Page 121) A. It may be due to diseases in intestinal mucosa, e.g. coeliac disease, sprue, Crohn’s disease.

94 Viva—based on Textbook of Biochemistry Q. Any other cause for defective absorption of fat? (Page 121) A. Any condition leading to a deficiency of bile salts can also result in malabsorption of fat. The most common causes are obstruction to biliary tract due to gall stones, tumours of head of pancreas, enlarged lymph glands, etc. Q. What is the line of management in defective absorption? (Page 121) A. In such cases, triglycerides with short chain and medium chain fatty acids are digested and absorbed properly, because they do not require micellerisation for absorption. Since milk fat and coconut oil are made up of MCT, they are therapeutically useful in malabsorption syndromes.

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Lipids-II:

Metabolism of Fatty acids, Fatty acid oxidation, Fatty acid synthesis, Lipolysis, Ketone bodies. Q. How fatty acids are activated in preparation of oxidation? (Page 122) A. Fatty acids are activated to their co-enzyme A (CoA) derivative. Q. What is the enzyme for this activation? (Page 122) A. Thiokinase or fatty acyl CoA synthetase. Q. How much ATP is required for this reaction? (Page 122) A. One molecule of ATP is hydrolysed to AMP and PPI. Thus two high energy bonds are utilised in this reaction. Q. What are the co-enzymes needed for fatty acid oxidation? (Page 122) A. FAD and NAD.

96 Viva—based on Textbook of Biochemistry Q. What is carnitine? (Page 122) A. Carnitine is beta-hydroxy-gamma-trimethyl ammonium butyrate. It is synthesised from lysine and methionine in liver and kidney. Q. What is the function of carnitine? (Page 122) A. Fatty acids are activated in the cytoplasm, but the beta-oxidation is in mitochondria. The long chain fatty acyl CoA cannot pass through the inner mitochondrial membrane. Therefore a transporter, carnitine is involved in transfer of fatty acids. Q. What about medium and small chain fatty acids? (Page 122) A. Medium chain fatty acids do not require carnitine for transport, so they are easily oxidised. Q. What is the net generation of ATP, when one molecule of palmitic acid (16 carbon) is oxidised completely? (Page 123) A. 129. Q. What are the products, during each cycle of beta oxidation of fatty acid? (Page 123) A. Acetyl CoA, FADH2, and NADH. Q. What are the energy producing steps in beta oxidation pathway? (Page 123) A. Fatty acyl CoA dehydrogenase (FAD) and beta hydroxy fatty acyl CoA dehydrogenase (NAD) steps. Q. What is the product of beta oxidation of odd chain fatty acids? (Page 124) A. Propionyl CoA.

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Q. What is the further metabolism of propionyl CoA? (Page 124) A. Propionyl CoA is first carboxylated to methyl malonyl CoA and then to form succinyl CoA. The succinyl CoA then enters TCA cycle. Q. What are the co-enzymes required for the conversion of propionyl CoA to succinyl CoA? (Page 124) A. Biotin, ATP, Vitamin B12. Q. Succinyl CoA is generated from which substances? (Page 124) A. Odd chain fatty acids, propionic acid, valine, isoleucine, threonine. Q. Succinyl CoA is utilised for what purposes? (Page 124) A. Porphyrin biosynthesis, activation of acetoacetate, and oxidation in TCA cycle. Q. What is alpha oxidation of fatty acid?(Page 124) A. It is a process by which fatty acids are oxidised by removing carbon atoms, one at a time, from the carboxyl end. It is used for fatty acids that have a methyl group at the beta-carbon, which blocks beta-oxidation. Alpha oxidation does not generate energy. Q. Where is alpha oxidation taking place? (Page 124) A. In endoplasmic reticulum (microsomes). Q. Refsum’s disease is due to what? (Page 125) A. Accumulation of phytanic acid, due to defective alpha oxidation.

98 Viva—based on Textbook of Biochemistry Q. What are the major differences between fatty acid synthesis and beta oxidation of fatty acid? (Page 125) A. Beta oxidation is taking place in mitochondria, fatty acid synthesis is in cytoplasm. Oxidation enzymes are independent, synthetic enzymes are grouped as a multi-enzyme complex. During oxidation, 2 carbon units are removed as acetyl CoA, during synthesis, 2 carbon units are added as 3 carbon malonyl CoA. For oxidation, NAD and FAD are necessary, for synthesis, NADPH is used. Q. How NADPH is made available? (Page 128) A. In the HMP shunt pathway, glucose-6-phosphate dehydrogenase reaction produces NADPH. Q. What is the rate limiting enzyme of de novo synthesis of fatty acid? (Page 126) A. Acetyl CoA carboxylase. Q. What is the reaction? (Page 126) A. Acetyl CoA + CO2 ® Malonyl CoA. Q. What are the co-enzymes required for the reaction? (Page 126) A. Biotin and ATP. Q. Acetyl CoA from mitochondria is transferred to cytoplasm for the de novo synthesis of fatty acid, by which enzyme? (Page 126) A. ATP citrate lyase. Q. What are the steps in which NADPH is used in fatty acid synthesis? (Page 127) A. Step 4 (Keto acyl reductase) and Step 6 (Enoyl reductase).

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Q. Acetyl CoA is used for what purposes? (Page 127) A. Fatty acid synthesis, oxidation in citric acid cycle for generation of energy, cholesterol synthesis and ketone body formation. Q. What are the sources of NADPH for fatty acid synthesis? (Page 128) A. Glucose-6-phosphate dehydrogenase, malic enzyme, cytoplasmic malate dehydrogenase. Q. How is fatty acid synthesis regulated? (Page 128) A. Key enzyme, acetyl CoA carboxylase, is stimulated by citrate and inhibited by palmitoyl CoA. Q. What is the action of insulin on fatty acid synthesis? (Page 128) A. Insulin favours lipogenesis. Q. How? (Page 128) A. Insulin enhances the uptake of glucose by adipocytes and increases the activity of pyruvate dehydrogenase. So, availability of acetyl CoA is increased. Insulin also activates glucose-6-phosphate dehydrogenase, so that enough NADPH is available. Moreover, insulin stimulates acetyl CoA carboxylase, the key enzyme of fatty acid synthesis pathway. (Table 10.3). Insulin also depresses the hormone sensitive lipase (Fig.13.11). Q. Chain elongation of fatty acid is taking place in which site? (Page 128) A. Microsomal elongation system is more active.

100 Viva—based on Textbook of Biochemistry Q. Triacyl glycerol synthesis is enhanced by which hormone? (Page 129) A. Insulin. Q. In adipose tissue, what is the source of glycerol phosphate for triglyceride formation?(Page 129) A. From dihydroxy acetone phosphate, derived from glucose. Q. White adipose tissue is concerned with what? (Page 129) A. Energy storage. Q. Brown adipose tissue is involved in what process? (Page 129) A. Thermogenesis. Q. What enzyme is involved in lipolysis? (Page 129) A. By hormone sensitive lipase. Q. What is its action? (Page 129) A. In adipose tissue, hormone sensitive lipase hydrolyses triglyceride into fatty acid and releases into blood. Q. In the blood, fatty acids are transported as what form? A. Albumin is the carrier of free fatty acid. Q. Hormone sensitive lipase is activated by which hormones? (Page 129) A. Growth hormone, corticosteroids, ACTH, adrenalin, and glucagon.

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Q. Which are the lipolytic hormones? (Page 129) A. Growth hormone, corticosteroids, ACTH, adrenalin, and glucagon. Q. What is the mechanism of activation of hormone sensitive lipase? (Page 129) A. A cascade through adenyl cyclase, cyclic AMP and kinase. Q. What is the action of caffeine? (Page 129) A. It inhibits phospho diesterase, increases activity of hormone sensitive lipase, and so, prolongs the action of cyclic AMP. Thus, caffeine favours lipolysis. Q. In diabetes mellitus, non-esterified fatty acid level in blood is increased, why? (Page 129) A. Insulin inhibits hormone sensitive lipase, in diabetes, this inhibition is removed, so, more lipolysis is taking place. Q. What worsens fatty liver? (Page 130) A. Alcohol, diabetes mellitus, excess calorie intake, hepatitis virus. Q. What are the sources of acetyl CoA? (Page 130) A. Pyruvate, fatty acids, acetoacetyl CoA, and leucine. Q. What substances will prevent fatty liver? (Page 131) A. Choline, methionine, lecithin. Q. What are ketone bodies? (Page 131) A. Aceto acetate, beta hydroxy butyric acid, and acetone.

102 Viva—based on Textbook of Biochemistry Q. Ketone bodies are formed in which tissue? (Page 131) A. Liver. Q. Ketogenesis is taking place in which subcellular organelle? (Page 131) A. Mitochondria. Q. What is the rate-limiting-step in ketone body formation? (Page 131) A. HMGCoA synthase. Q. HMGCoA is directly converted into what substances? (Page 131) A. Acetoacetate, acetyl CoA, mevalonate. Q. Ketone body utilisation is taking place in which organs? (Page 131) A. Ketolysis is taking place in extra hepatic tissues. (All other tissues, except liver). Q. Utilisation of ketone bodies by peripheral tissues needs which enzyme? (Page 131) A. Succinyl CoA dependent thiophorase. Q. Ketosis is due to what processes? (Page 132) A. Step 1: Absence of insulin leads to excessive hydrolysis of triacyl glycerol. Step 2: So more fatty acid is available, and more acetyl CoA is produced. Step 3: But oxidation of acetyl CoA in citric acid cycle is sluggish. The excess acetyl CoA is diverted into ketone body formation. Q. What test is used to identify ketone bodies in urine? (Page 132) A. Rothera’s test.

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Lipids-III:

Cholesterol, Lipoproteins and Cardiovascular Diseases

Q. What is the ring structure present in cholesterol? (Page 133) A. Perhydro cyclo pentano phenanthrene ring. Q. Cholesterol has how many carbon atoms? (Page 133) A. It has 27 carbon atoms. Q. What are the substances derived from cholesterol? (Page 133) A. Glucocorticoids, mineralocorticoids, testosterone, estrogen, bile acids. Q. Which food stuffs contain cholesterol? (Page 133) A. Non-vegetarian food. Q. Whether cholesterol is present in vegetable oils? (Page 133) A. No.

104 Viva—based on Textbook of Biochemistry Q. What is the rate-limiting-step in the cholesterol biosynthesis? (Page 134) A. HMG CoA reductase. Q. What is HMG CoA synthase? (Page 131) A. It is the rate-limiting-enzyme in ketogenesis pathway. Q. What is the first sterol ring formed during cholesterol biosynthesis? (Page 134) A. Lanosterol. Q. How cholesterol is excreted? (Page 135) A. Through bile, partly as cholesterol itself, and partly as bile salts. Q. What is the normal level of total plasma lipids? (Page 135) A. 400-600 mg/dl. Q. What is the normal level of total cholesterol? (Page 135) A. 150-220 mg/dl. Q. What is the normal level of triglycerides? (Page 135) A. 50-200 mg/dl. Q. How lipoproteins are estimated? (Page 136) A. Either by electrophoresis or by ultracentrifugation. Q. During electrophoresis, what is the fastest moving lipoprotein? (Page 136) A. HDL (alpha lipoprotein).

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Q. During electrophoresis, what is the least moving lipoprotein? (Page 136) A. Chylomicron (gamma position). Q. Maximum cholesterol content is in which lipoprotein? (Page 136) A. LDL (Beta lipoprotein). Q. Triglycerides present in chylomicrons are hydrolysed by what? (Page 137) A. Lipoprotein lipase. Q. Where is the enzyme present? (Page 137) A. It is located at the endothelial layer of capillaries of adipose tissue, muscles and heart, but not in liver. Q. What is the main apoprotein present in chylomicron. (Page 137) A. B48. Q. What is the function of chylomicron? (Page 137) A. Transport of triglycerides from intestine to adipose tissue. Q. Highest content of triglycerides is seen in which lipoprotein? (Page 137) A. Chylomicrons. Q. Endogenous triglycerides in plasma are carried by what? (Page 138) A. VLDL. Q. What is the main apoprotein present in LDL? (Page 138) A. B100, it is the ligand for LDL receptor.

106 Viva—based on Textbook of Biochemistry Q. What is the function of LDL receptors? (Page 138) A. LDL receptors are present on all cells but most abundant in hepatic cells and adrenal cortex. LDL receptors, located in specialised regions called clathrin-coated pits. When the apo B-100 binds to the receptor, the receptor-LDL complex is internalised by endocytosis. Q. What is the function of LDL? (Page 138) A. Transport of cholesterol from liver to peripheral tissues. Q. What is “bad cholesterol”? A. LDL cholesterol.

(Page 139)

Q. Why it is called so? (Page 139) A. LDL transports cholesterol from liver to peripheral tissues, where it is deposited, and causes atherosclerosis. Q. What is lipoprotein(a) ? (Page 139) A. It is attached to apo B-100 by a disulfide bond. It has significant homology with plasminogen. So it interferes with plasminogen activation and impairs fibrinolysis (Fig.14.10). This leads to unopposed intravascular thrombosis and possible myocardial infarction. Q. What is the significance of lipoprotein (a)? (Page 139) A. Lp(a) is associated with heart attacks at the age of 30 or 40 years. Indians have a higher level of Lp(a) than Europeans.

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Q. What is the normal level of lipoprotein (a) ? (Page 139) A. In 40% population, there is no detectable level of Lp(a) in serum. In 20% of population, the Lp(a) concentration in blood is more than 30 mg/dl, and these persons are susceptible to heart attack at a younger age. Q. What is the function of HDL? (Page 139) A. Transport of cholesterol from peripheral tissues to liver. Q. What is “good cholesterol”? A. HDL cholesterol.

(Page 139)

Q. Why it is called so? (Page 139) A. HDL transports cholesterol from peripheral tissues to liver, and so helps in excretion of cholesterol from the body. So HDL is anti-atherogenic. Q. What is the main apoprotein present in HDL? (Page 139) A. Apo A-1, it is the ligand for HDL receptor. Q. What is LCAT? (Page 139) A. Lecithin cholesterol acyl transferase. Q. Where is it present? (Page 139) A. LCAT present in plasma is activated by apo-A1, when LCAT binds to HDL disc. Q. What is its importance? (Page 139) A. The free cholesterol is esterified by LCAT the esterified cholesterol is then incorporated into HDL disc, to form mature HDL. So for excretion of cholesterol, LCAT is necessary.

108 Viva—based on Textbook of Biochemistry Q. What is the importance of PUFA in cholesterol metabolsim? (Page 140) A. PUFA present in lecithin is transferred to cholesterol by the enzyme LCAT. The esterified cholesterol is then taken by HDL, and finally excreted through liver. So, for excretion of cholesterol, PUFA is required. Thus, PUFA will lower the blood level of cholesterol. Q. Free fatty acids of plasma are bound to what? (Page 140) A. Bound to serum albumin. Q. What is the function of albumin? (Page 140) A. Transport of free fatty acid from adipose tissue to peripheral tissues. Q. Triglycerides present in adipose tissue are hydrolysed by what enzyme? (Page 140) A. Hormone sensitive lipase. Q. What are the salient features of hyperlipoproteinemia Type II-A? (Page 141) A. Premature atherosclerosis elevated plasma LDL cholesterol, and prominent beta band on electrophoresis. Q. What is it due to? A. Defect in LDL receptor.

(Page 141)

Q. What is the treatment policy? (Page 141) A. Low cholesterol diet, decreased intake of saturated fat, increased intake of PUFA, bile acid binding resins.

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Q. What is the normal serum cholesterol level? (Page 142) A. 150-220 mg/dl. Q. Hypercholesterolemia is seen in what conditions? (Page 143) A. Diabetes mellitus, nephrotic syndrome, obstructive jaundice, hypothyroidism. Q. How atherosclerosis started? (Page 143) A. The effect is directly proportional to the LDL levels. Free radical induced oxidative damage of LDL will accelerate this process. Oxidised LDLcholesterol is deposited in the subintimal regions of arteries. Q. What tissues are affected mostly by atherosclerosis? (Page 143) A. Aorta, coronary arteries and cerebral vessels are predominantly affected. Q. How LDL deposit leads to atherosclerosis? (Page 143) A. Oxidised LDL is taken up by macrophages, the macrophages become overloaded with cholesterol esters, and these are then called “foam cells” which form the hallmark of atherosclerotic plaques. Q. What happens to atherosclerotic plaque? (Page 143) A. This leads to narrowing of vessel wall. Then fibrous proliferation takes place, this is due to liberation of various growth factors. Again a clot is formed which occludes one of the major vessels. Then there is ischemia of the tissue supplied. Finally infarction or ischemic death of the tissue occurs.

110 Viva—based on Textbook of Biochemistry Q. What are the important risk factors of coronary artery diseases? (Page 144) A. Serum cholesterol level above 220 mg/dl, LDLcholesterol level above 160 mg/dl, HDL-cholesterol level below 35 mg/dl, and Apo(a) above 30 mg/dl. Q. What are other risk factors associated with coronary artery diseases? (Page 144) A. Cigarette smoking, hypertension, diabetes mellitus, serum triglyceride level above 200 mg/dl, homocysteine level, sedentary life style, obesity. Q. What advise you will give to a person with increased cholesterol level? (Page 144) A. Reduce food with higher cholesterol content of food, include PUFA and omega-3 fatty acids in diet, reduction of total fat intake of green leafy vegetables, exercise, avoid cigarettes. Q. When will you start drugs for a person with increased cholesterol level? (Page 144) A. When patient’s condition is not responding to the dietary restriction. Q. What are the drugs available to treat hypercholesterolemia? (Page 144) A. Bile acid binding recins, HMGCoA reductase inhibitors, fibrate derivatives, nicotinic acid. Q. What is the function of bile acids? (Page 146) A. They are the major route of excretion of cholesterol and they are required for absorption of triacyl glycerol.

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Q. Bile acids are derived from what substance? (Page 146) A. Cholesterol. Q. How are bile salts formed? (Page 146) A. Bile acids conjugated with taurine or glycine.

112 Viva—based on Textbook of Biochemistry

Lipids-IV:

MCFA, PUFA and Prostaglandins

Q. What is MCFA? (Page 147) A. Medium chain fatty acids they contain 8 to 14 carbon atoms. Q. What is LCFA? (Page 147) A. Long chain fatty acids they contain 16 to 18 carbon atoms. Q. What is VLCFA? (Page 147) A. Very long chain fatty acids they contain 20 or more carbon atoms. Q. What is the difference in digestion of MCT from that of LCFA? A. MCT containing triglycerides are digested by MCT-specific lipase. Pancreatic lipase and bile salts are not required. (Page 147)

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Q. What is the difference in absorption of MCFA from that of LCFA? A. MCFA is absorbed directly to blood (not to lacteals, as in the case of LCFA). Further, after absorption, MCFA is carried by albumin in blood, whereas LCFA are absorbed as triglycerides and carried by chilomicrons. (Page 147) Q. So what is the advantage of MCFA? (Page 147) A. MCFA are easily digested, easily absorbed, and easily oxidised (when compared to LCFA). Q. When palmitoleic acid (16 C, 1 double bond) is completely oxidised, what is the net generation of ATP molecules? (Page 147) A. 127. Q. When unsaturated fatty acids are oxidised, how many ATP is formed? A. The energy yield is less by 2 ATP molecules per double bond, when compared to the corresponding chain length saturated fatty acid. (Page 147) Q. Why 2 ATP molecules are reduced? (Page 147) A. Because, the FAD dependent dehydrogenation (step 1 of beta oxidation) does not occur at the double bond. Q. Name polyunsaturated fatty acids. (Page 147) A. Linoleic, linolenic and arachidonic acids. Q. What are essential fatty acids? (Page 148) A. Those cannot be synthesised by the body. So they are to be provided in the diet.

114 Viva—based on Textbook of Biochemistry Q. Name the essential fatty acids. (Page 148) A. Linoleic and linolenic acids are the only fatty acids which cannot be synthesised in the body. Q. Where does desaturation of fatty acid takes place? (Page 148) A. In the endoplasmic reticulum. Q. What is the enzyme called? A. Microsomal desaturase system.

(Page 148)

Q. What are the important substances derived from PUFA? (Page 148) A. Prostaglandins, prostacycline, thromboxanes, leukotienes, HPETE. Q. What are the functions of PUFA? (Page 148) A. Synthesis of prostaglandins, synthesis of phospholipids and esterification of cholesterol. Q. How prostaglandins are classified? (Page 149) A. According to the attachment of different substituent groups to the ring, PGs are named with capital letters such as A, B, E and F. In the same series, depending on number of double bonds on the side chains they are denoted by a subscript after the capital letter, e.g. PGE1, PGE2, PGE3, etc. Series 2 have two double bonds at 13-14 (trans) and 5-6 (cis). This is the most common variety. Q. Prostaglandins are derived from what substance? (Page 149) A. Prostaglandins are derived from the PUFA. The Series 2 (with two double bonds) are derived from arachidonic acid. All naturally occurring PGs belong to the 2-series.

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Q. Prostaglandins are stored in what form? (Page 149) A. As precursors, as membrane phospholipids. Q. How prostaglandins are synthesised?(Page 149) A. The arachidonic acid is released by the action of phospholipase A2 on phospholipids prostaglandin synthesis is catalysed by prostaglandin H synthase (PGHS). It contains two separate enzyme activities, cyclo-oxygenase and peroxidase. Q. How prostaglandin synthesis is regulated? (Page 150) A. The phospholipase is activated by epinephrine. Steroids inhibit PL and prevent release of arachidonic acid from membranes. Q. What is the importance of cyclo-oxygenase? (Page 150) A. Cyclo-oxygenase is activated by catecholamines and inhibited by non-steroid anti-inflammatory drugs (NSAIDS). Cyclo-oxygenase is a “suicide” enzyme. Q. What is the mechanism of action of aspirin? (Page 150) A. Aspirin acetylates serine in the active site and irreversibly inhibits the cyclo-oxygenase. Q. How is prostaglandins inactivated? (Page 150) A. Prostaglandins have only very short half life, of about 30 seconds. They are inactivated by the 15hydroxy-prostaglandin-dehydrogenase which converts 15-OH group to keto group.

116 Viva—based on Textbook of Biochemistry Q. What is the mechanism of action of prostaglandins? (Page 150) A. Prostaglandins are local hormones, and function through G-protein coupled receptors In most tissues, PGE increases cAMP level. But in adipose tissue and in renal tubular cells, PGE lowers cAMP level. Q. What is the action of prostacyclin on vascular endothelium? (Page 150) A. Prostacyclin causes vasodilatation. It also inhibits platelet aggregation and has a protective effect on vessel wall against deposition of platelets. Q. What is the effect of thromboxane?

(Page 150)

A. Thromboxane (TXA2) is the main PG produced by platelets. The major effects are vasoconstriction and platelet aggregation. Prostacyclin and thromboxane are opposing in activity. Q. What is the precursor of leukotrienes? (Page 151) A. They are produced from arachidonic acid. Q. What is its biological importance? (Page 151) A. LT B4 is produced in neutrophils, it is the most potent chemotactic agent. The slow reacting substance of anaphylaxis (SRS-A) contains LTC4, LTD4 and LTE4. They cause smooth muscle contraction, constrict the bronchioles, increase capillary permeability and produce vasoconstriction.

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Q. What are VLCFAs? (Page 151) A. Fatty acids having 20 or more carbon atoms are called very long chain fatty acids (VLCFA). Eicosa penta-enoic acid (EPA) (Timnodonic acid, C-20, 5 double bonds) and docosa hexa-enoic acid (DHA) (cervonic acid, C-22, 6 double bonds) are good examples of VLCFA. Q. What is the importance of DHA? (Page 151) A. DHA is synthesised linolenic acid. DHA can be obtained from fish oils or from milk. DHA is especially required for the development of brain and retina. Low levels of DHA in blood is seen in patients with retinitis pigmentosa.

118 Viva—based on Textbook of Biochemistry

Lipids-V:

Compound Lipids

Q. How phospholipids are classified? (Page 152) A. 1. Nitrogen containing glycero phosphatides, 2. Non-nitrogen containing glycero phosphatides, 3. Plasmalogens, 4. Phospho sphingosides 5. Glycosphingolipids 6. Sulpholipids. Q. What is Lecithin? A. Phosphatidyl choline.

(Page 152)

Q. What is phosphatidic acid? (Page 152) A. Phosphatidic acid is made up of one glycerol to which two fatty acid residues are esterified to carbon atoms 1 and 2 and the 3rd hydroxyl group is esterified to a phosphoric acid. Q. What is Cephalin? A. Phosphatidyl ethanol amine.

(Page 152)

Lipids-V

Q. What is Cardiolipin? A. Diphosphatidyl glycerol.

119

(Page 152)

Q. What is sphingomyelin? (Page 154) A. All sphingolipids have the long aliphatic aminoalcohol sphingosine which is attached to a fatty acid in amide linkage to form a ceramide. A common phosphosphingoside present abundantly in the nervous system, is sphingomyelin. It contains choline. Sphingomyelins are the only sphingolipid that contain phosphate and have no sugar moiety. Q. What is a cerebroside? A. Ceramide monohexoside.

(Page 154)

Q. What is a globoside? A. Ceramide oligosaccharides.

(Page 154)

Q. What is lung surfactant? (Page 153) A. It is produced by lung epithelial cells. Surfactant decreases surface tension of the aqueous layer of lung and prevents collapse of lung alveoli. Q. What are the constituents of surfactants? (Page 153) A. Surfactants contain dipalmitoyl lecithin, phosphatidyl glycerol, cholesterol and surfactant proteins A, B and C. Q. What is its clinical significance? (Page 153) A. Low levels of surfactant leads to respiratory distress syndrome (RDS), which is a common cause of neonatal morbidity.

120 Viva—based on Textbook of Biochemistry Q. Phospholipids can aggregate into what ? (Page 153) A. Micelle and liposome. Q. What is the nitrogenous base present in lecithin? (Page 153) A. Choline. Q. Cerebroside contains what? A. Sphingosine, fatty acid, hexose.

(Page 154)

Q. On hydrolysis of sphingomyelin, what are obtained? (Page 154) A. Sphingosine, fatty acid, phosphoric acid, choline. Q. A ganglioside on hydrolysis, will give rise to what? (Page 154) A. Sphingosine, fatty acid, N-acetyl neuraminic acid. Q. Name some lipid storage diseases. (Page 156) A. Tay Sach’s disease, Niemann Pick’s disease, Gaucher’s disease. Q. Gaucher’s disease is due to the deficiency of what? (Page 157) A. Beta glucosidase. Q. What is accumulated in Gaucher’s disease? (Page 157) A. Glucocerebroside. Q. Niemann-Pick disease is due to the deficiency of what? (Page 157) A. Sphingomyelinase.

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Q. What is accumulated in Niemann-Pick disease? (Page 157) A. Sphingomyelin. Q. Tay Sach’s disease is due to the deficiency of what? (Page 157) A. Hexosaminidase. Q. What is accumulated in Tay Sach’s disease? (Page 157) A. Ganglioside.

122 Viva—based on Textbook of Biochemistry

Amino Acid Metabolism-I:

General: Digestion, Absorption, Transamination, Urea Q. What is the enzyme mainly responsible for protein digestion in stomach? (Page 158) A. Pepsin. Q. What is the action of pepsin? (Page 158) A. It hydrolyses peptide bonds formed by carboxyl groups of phenyl alanine, tyrosine, tryptophan and methionine. Q. How pepsinogen is activated? (Page 158) A. Removal of N-terminal end by gastric hydrochloric acid. Q. What are zymogens? (Page 158) A. They are pro-enzymes, inactive at the time of secretion, but will be activated in the gastro intestinal tract.

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Q. How the activation is effected generally? (Page 158) A. Activation is achieved by removing a small part of the precursor molecules. Selective proteolysis produces the catalytic site. Q. What is its biological significance? (Page 158) A. Zymogens prevent autodigestion of the cells. Q. What is its clinical significance? (Page 158) A. Acute pancreatitis results when trypsinogen is activated prematurely. Q. What are important enzymes in pancreatic juice? (Page 158) A. Pancreatic juice contains the endopeptidases trypsin, chymotrypsin and elastase. Q. How trypsinogen is activated? (Page 159) A. The activation of trypsinogen is by removal of a hexapeptide from N-terminal end by entero-kinase (enteropeptidase) present on the intestinal microvillus membranes. Q. What is the action of trypsin? (Page 159) A. It hydrolyses peptide bonds formed by carboxyl groups of arginine and lysine. Q. How chymotrypsinogen is activated? (Page 159) A. It is activated by trypsin. Q. What is an endopeptidase? (Page 159) A. It acts on peptide bonds inside the protein molecule, so that the protein becomes successively smaller and smaller units.

124 Viva—based on Textbook of Biochemistry Q. Give some examples of an endopeptidase. (Page 159) A. Trypsin, pepsin. Q. What are exopeptidases? (Page 159) A. They act at one of the protein molecule, liberating amino acids sequentially, one at a time. Q. Give an example exopepdases. A. Carboxypeptidase.

(Page 159)

Q. What is carboxypeptidase? (Page 159) A. It is secreted by cells of intestinal villi, it is a metallo-enzyme containing zinc, it is an endopeptidase, spliting off carboxy terminal bond of the protein. Q. What is required for absorption of amino acids? (Page 160) A. It needs the help of glutathione. Q. What are cathepsins? A. Intracellular proteases.

(Page 160)

Q. What is ubiquitin? (Page 160) A. It is necessary for intracellular protein breakdown. Q. What are proteosomes? (Page 160) A. Ubiquitin tagged proteins are degraded inside the cells, with the help of proteosomes. Q. In fasting state, nitrogen is transported from muscle as what form? A. In the fasting state, the muscle releases mainly alanine and glutamine of which alanine is taken up by liver and glutamine by kidneys.(Page 160)

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Q. Transamination of glutamic acid produces what? (Page 161) A. Alpha keto glutaric acid. Q. What is the co-enzyme necessary for transamination reaction? A. Pyridoxal phosphate. (Page 161) Q. What are the physiological significance of transamination? (Page 161) A. It synthesises non-essential amino acids, it helps in the equalisation of quantities of amino acids, it is the first step of amino acid breaking down pathways. Q. What is the clinical significance of transamination? (Page 161) A. Transaminases are increased in blood in liver and cardiac diseases. Q. What is transdeamination? (Page 161) A. Transamination takes place in all the cells of the body, the amino group is transported to liver as glutamic acid which is finally oxidatively deaminated in liver. Thus, the two components of the reaction are physically far away, but physiologically they are coupled. Hence the term transdeamination. Q. Transamination reaction of pyruvate with glutamate results in the production of what substances? (Page 161) A. Alanine and alpha keto glutarate.

126 Viva—based on Textbook of Biochemistry Q. Which amino acid is oxidatively deaminated in liver? (Page 162) A. Glutamic acid. Q. What is the reaction catalysed by glutamate dehydrogenase? A. Glutamate alpha keto glutarate + ammonia. (Page 162) Q. What is the co-enzyme required for glutamate dehydrogenase? A. NAD. (Page 162) Q. Nitrogen atoms in the urea is derived from what precursors? A. One from ammonia and another from aspartic acid. (Page 163) Q. Ammonia is immediately trapped in brain by what? (Page 163) A. Glutamine synthetase. Q. What is the reaction catalysed by glutamine synthetase? (Page 163) A. Glutamic acid + ammonia ® glutamine, this requires hydrolysis of ATP to ADP. Q. What is the key enzyme of urea synthesis? (Page 163) A. Carbamoyl phosphate synthetase. Q. What are the two carbamoyl phosphate synthetases? (Page 164) A. CPS-I is involved in urea synthesis, CPS-II is required for pyrimidine synthesis. CPS-I is seen in mitochondria, while CPS-II is in cytosol.

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Q. What is the normal blood urea level? (Page 165) A. 20-40 mg/dl. Q. Blood urea level is markedly increased in which condition? (Page 165) A. Renal diseases. Q. What is the normal urinary excretion of urea? (Page 165) A. 15-30 mg/day.

128 Viva—based on Textbook of Biochemistry

Amino Acid Metabolism-II:

Simple, Hydroxy and Sulfur Containing Amino Acids Glycine, Serine, Alanine, Threonine, Methionine, Cysteine Q. Glycine is used for synthesis of what compounds? (Page 166) A. Serine, Creatine, Purines, Heme, Glutathione, Bile salts. Q. For creatine synthesis, which amino acids are used? (Page 167) A. Glycine, arginine, methionine. Q. Guanido acetic acid is formed in which tissue? (Page 167) A. Kidney. Q. Guanido acetic acid is formed from what amino acids? (Page 167) A. Arginine + glycine.

Amino Acid Metabolism-II

Q. Where is creatine is synthesised? A. In liver.

129

(Page 167)

Q. What is the significance of creatinine?(Page 167) A. Excretion is increased in muscle dystrophy. Q. How creatinine is produced in the body? (Page 167) A. By spontaneous degradation of creatine phosphate. Q. What are the sources of oxalic acid in urine? (Page 168) A. Ascorbic acid and glycine. Q. What is the cause of hyper oxaluria? (Page 168) A. Protein targeting defect. Q. What are the important substances produced from serine? (Page 168) A. Glycine, pyruvate,cysteine,selenocysteine, choline, phosphatidyl serine. Q. On decarboxylation, serine will produce what? (Page 169) A. Ethanol amine. Q. Choline is derived from what? A. Serine.

(Page 169)

Q. What is the product of transamination of alanine? (Page 169) A. Pyruvic acid.

130 Viva—based on Textbook of Biochemistry Q. What is the significance of glucose-alanine cycle? (Page 169) A. During starvation, alanine is released from muscle, and is taken up by liver. In liver alanine is transaminated to pyruvate, and pyruvate undergoes gluconeogenesis. Q. What are important substrates for transmethylation reactions? (Page 170) A. Guanido acetic acid, serine, nor-epinephrine, Nacetyl serotonin. Q. What is the methyl donor in transmethylation reaction? (Page 170) A. S-adenosyl methionine. Q. Which amino acid has two optically active (asymmetric) carbon atom? (Page 170) A. Threonine. Q. What are the functions of glutathione? (Page 171) A. Reduction of met-hemoglobin to hemoglobin, keeping RBC membrane integrity, carrying amino acids across membranes, and detoxification of peroxidases. Q. What is glutathione? A. Gamma glutamyl cysteinyl glycine.

(Page 171)

Q. Urine of a patient with homocystinuria will be positive for which test? A. Cyanide nitroprusside test. (Page 173)

Amino Acid Metabolism-II

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Q. What is the defective enzyme in homocystinuria? (Page 173) A. Cystathionine synthase. Q. What are the characteristic features of homocystinuria? (Page 173) A. Mental retardation, subluxation of lens, and thrombosis. Q. Homocystinuria is due to abnormal metabolism of which amino acid? (Page 173) A. Methionine. Q. What is the defective enzyme in Cystathionuria? (Page 173) A. Cystathionase.

132 Viva—based on Textbook of Biochemistry

Amino Acid Metabolism-III:

Acidic, Basic and Branched Chain Amino Acids, Glutamic acid, Glutamine, Aspartic acid, Asparagine, Lysine, Nitric Oxide, Valine, Leucine, Isoleucine Q. What are the major functions of glutamic acid? (Page 175) A. Transamination, transdeamination, ammonia trapping in brain, and production of gamma amino butyric acid. Q. Transamination reaction of pyruvate with glutamate results in the production of what substances? (Page 175) A. Alanine and alpha keto glutarate. Q. Which amino acid is oxidatively deaminated in liver? (Page 175) A. Glutamic acid. Q. What is the reaction catalysed by glutamate dehydrogenase? A. Glutamate ® alpha keto glutarate + ammonia. (Page 175)

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Q. What is the co-enzyme required for glutamate dehydrogenase? A. NAD. (Page 175) Q. Ammonia is immediately trapped in brain by what? (Page 175) A. Glutamine synthetase. Q. What is the reaction catalysed by glutamine synthetase? (Page 175) A. Glutamic acid + ammonia ® glutamine, this requires hydrolysis of ATP to ADP. Q. What is the reaction catalysed by glutaminase? (Page 176) A. Glutamine ® glutamic acid + ammonia. Q. Glutaminase enzyme is used for what purpose? (Page 175) A. Excretion of ammonia in kidney tubules. Q. Transamination of glutamic acid will give rise to what? A. Alpha keto glutarate. Q. Decarboxylation of glutamic acid will give rise to what? A. Gamma amino butyric acid. Q. What is GABA? A. It is an inhibitory neurotransmitter. Which is produced by decarboxylation of glutamic acid. Q. Which will give rise to an inhibitory neurotransmitter? (Page 175) A. Glutamic acid.

134 Viva—based on Textbook of Biochemistry Q. Glutamic acid can be formed from which amino acids? (Page 175) A. Histidine, arginine, proline, glutamine. Q. Transamination of pyruvic acid will give rise to what? (Page 175) A. Alanine. Q. Transamination of oxaloacetic acid will give rise to what? (Page 175) A. Aspartic acid. Q. What are the functions of glutamine? (Page 176) A. Ammonia trapping in brain (glutamic acid + ammonia to glutamine), ammonia production in kidney (glutamine to glutamic acid + ammonia), synthesis of purine (Nitrogen 3 and 9), synthesis of pyrimidine (3rd Nitrogen), synthesis of guanine and cytosine (amino groups). Q. Alpha amino group of aspartic acid is incorporated into which compounds? (Page 176) A. Purines (1st nitrogen and 6th amino), pyrimidines (1st nitrogen and C4,5,6), and urea. Q. Which amino acids are required for both purine and pyrimidine synthesis? (Page 176) A. Aspartic acid, glutamine. Q. What is asparaginase? (Page 176) A. Enzyme catalysing the reaction asparaginase to aspartic acid + ammonia. Q. What is its function? (Page 176) A. Ammonia production in kidney tubules.

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Q. What is its clinical application? (Page 176) A. It is an anticancer drug against leukemias and lymphomas. The leukemia cells cannot synthesis glutamine, and the available glutamine is destroyed by glutaminase, leukemia cells will starve and die. Q. Lysine is deficient in which food stuffs? (Page 176) A. Lysine is deficient in cereals. Q. Carnitine is synthesised from which amino acid? (Page 177) A. Lysine. Q. Nitric oxide synthase system needs which coenzymes? (Page 178) A. FAD, FMN, tetra hydro biopterine, NADPH. Q. What are the iso-enzymes of nitric oxide synthase? (Page 178) A. Neuronal NOS, inducible NOS (macrophages) and endothelial NOS. Q. What are the major functions of nitric oxide? (Page 178) A. Vasodilatation, keeping the normal blood pressure, inhibitioin of adhesion of platelets, memory process in brain, bactericidal in macrophages. Q. What is the precursor of nitric oxide? (Page 178) A. Arginine. Q. Which will give rise to polyamines? (Page 179) A. Ornithine.

136 Viva—based on Textbook of Biochemistry Q. What are polyamines? (Page 179) A. Polyamines are putrescine, spermine and spermidine. Q. What are the functions of polyamines? (Page 179) A. They are growth factors, their concentration is increased in cancer. Q. Name some mono amines. (Page 180) A. Histamine, dopamine, and serotonin. Q. What about glutamine? Is it an amine? (Page 180) A. No. Glutamine is an amide of glutamic acid. Q. Valine enters in which metabolism? (Page 180) A. Valine is glucogenic. Q. Leucine enters in which metabolism?(Page 180) A. Leucine is ketogenic. Q. Isoleucine joins in which metabolism? (Page 180) A. Isoleucine is partly glucogenic and partly ketogenic. Q. Branched chain keto acids are excreted in urine in what condition? A. Maple syrup urine disease. (Page 180) Q. What is the defect in maple syrup urine disease? (Page 180) A. Deficient decarboxylation of branched chain keto acids.

Amino Acid Metabolism-IV

137

Amino Acid Metabolism-IV:

Aromatic Amino Acids: Phenyl alanine, Tyrosine, Tryptophan, Histidine Q. Which amino acids are both glucogenic and ketogenic? (Page 181) A. Phenyl alanine, tyrosine, tryptophan, and isoleucine. Q. What are the important substances synthesised from tyrosine? A. Melanin, thyroxine, epinephrine and norepinephrine. (Page 182) Q. What is the immediate precursor of norepinephrine? (Page 182) A. Dopamine. Q. In pheochromocytoma, urine contains what substance? (Page 183) A. Vanillyl mandelic acid.

138 Viva—based on Textbook of Biochemistry Q. Phenyl alanine level in blood is increased in what condition? A. Phenyl ketonuria. (Page 183) Q. What is the defective enzyme in phenyl ketonuria? (Page 183) A. Phenyl alanine hydroxylase. Q. What are the co-enzymes required for phenyl alanine hydroxylase? A. NADH, NADPH, tetrahydro bioptrin. (Page 181) Q. Phenyl alanine, on transamination will give rise to what? (Page 183) A. Phenyl pyruvate. Q. What are the salient features of phenylketonuria? (Page 184) A. Mental retardation, hyperactivity, high blood phenyl alanine. Q. Phenyl pyruvic acid is excreted in urine in which condition? A. Phenyl ketonuria. (Page 184) Q. Homogentisic acid is excreted in urine in which condition? A. Alkaptonuria. (Page 184) Q. What is the defective enzyme in alkaptonuria? (Page 184) A. Homogentisic acid oxidase. Q. Ochronosis is a manifestation of which condition? (Page 184) A. Alkaptonuria.

Amino Acid Metabolism-IV

139

Q. What is associated manifestation of albinism? (Page 184) A. Nystagmus. Q. A person’s urine was found to turn black on standing and gave a positive Benedict’s test. He is likely to have what condition? (Page 184) A. Alkaptonuria. Q. In phenyl ketonuria, urine will be positive for what test? (Page 184) A. Ferric chloride test. Q. What is the defect in tyrosinemia type I (hepatorenal tyrosinemia)? A. Fumaryl acetoacetate hydrolase deficiency. (Page 185) Q. What is the defect in tyrosinemia type II (oculocutaneous tyrosinemia? (Page 185) A. Deficiency of tyrosine amino transferase. Q. Tryptophan is deficient in which food stuff? (Page 185) A. Maize and corn. Q. Xanthurenic acid in urine is seen in which condition? (Page 185) A. Pyridoxal deficiency. Q. What are the important substances produced from tryptophan? A. Serotonin, melatonin, niacin, alanine, and acetoacetate. (Page 186)

140 Viva—based on Textbook of Biochemistry Q. Which amino acid will give rise to a vitamin? (Page 186) A. Tryptophan. Q. Serotonin is derived from which amino acid? (Page 186) A. Tryptophan. Q. What are the characteristic features of malignant carcinoid syndrome (argentaffinoma)?(Page 186) A. Niacin deficiency, increased serotonin production, increased hydroxy indole acetic acid excretion, fluctuating hypertension. Q. Pellagra is manifested in which conditions? (Page 186) A. Niacin deficiency, pyridoxal deficiency, tryptophan deficiency, and carcinoid syndrome. Q. What is Hartnup’s disease? (Page 188) A. Absorption of aromatic amino acids from intestine as well as reabsorption from renal tubules are defective. So tryptophan deficiency, and pellagralike symptoms are seen. Q. Tryptophan is excreted in large quantities in which condition? A. Hartnup’s disease. (Page 188) Q. In Hartnup’s disease, which test will give a positive test? (Page 188) A. Obermeyer test will be positive in urine.

Amino Acid Metabolism-IV

141

Q. Indican in urine is tested by what method? (Page 188) A. Obermeyer test. Q. What is indican? A. Putrefaction product of tryptophan.

(Page 187)

Q. What is the amino acid which has maximum buffering capacity at physiological pH? (Page 188) A. Histidine. Q. What is the decarboxylation product of histidine? (Page 188) A. Histamine. Q. Which is the vasodialator produced from histidine? (Page 188) A. Histamine. Q. What is the clinical significance of histamine? (Page 188) A. It is a powerful vasodilator and mediator of anaphylaxis. Q. What is Figlu excretion test? (Page 189) A. In folic acid deficiency, there is a block in histidine metabolism, and figlu is excreted in large quantities in urine. Q. What is figlu? (Page 189) A. Formimino glutamic acid, it is a product of histidine metabolism.

142 Viva—based on Textbook of Biochemistry

Amino Acid Metabolism-V:

Inter-relations of amino acid metabolisms, One carbon metabolism, Amino acidurias Q. Tetra hydro folic acid is used for what purpose? (Page 190) A. It is the carrier of one carbon compounds. Q. Name one carbon compounds? (Page 190) A. Formyl, formimino, methenyl, hydroxymethyl, methylene, and methyl. Q. Which are the donors to one carbon pool? (Page 191) A. Serine, choline, glycine, tryptophan, histidine. Q. One carbon units are used for synthesis of what? (Page 191) A. C2 of purine, C8 of purine, serine, dTMP, choline, creatine, epinephrine.

Amino Acid Metabolism-V Citric Acid Cycle

143 143

Q. Which is the purely ketogenic amino acid? (Page 192) A. Leucine. Q. What are partially ketogenic and partially glucogenic amino acids? A. Phenyl alanine, tyrosine, tryptophan, isoleucine. (Page 192) Q. What are important aminoacidurias which cause mental retardation? (Page 192) A. Phenyl ketonuria, homocystinuria, maple syrup urine disease. Q. What is the defect in phenylketonuria? (Page 192) A. Deficiency of phenyl alanine hydroxylase. Q. What is the defect in alkaptonuria? (Page 192) A. Deficiency of homogentisic acid oxidase. Q. What is the defect in homocystinuria (type 1)? (Page 192) A. Deficiency of cystathionine beta synthase. Q. What is the defect in maple syrup urine disease? (Page 193) A. Deficiency of branched chain keto acid decarboxylase. Q. What is the defect in cystathionuria? (Page 193) A. Deficiency of cystathionase.

144 Viva—based on Textbook of Biochemistry

Citric Acid Cycle Q. What are the steps in which carbon dioxide is liberated, during the oxidation of glucose? (Page 195) A. Pyruvate dehydrogenase, isocitrate dehydrogenase, alpha keto glutarate dehydrogenase. Q. Acetyl CoA is produced from what substrates? (Page 194) A. Pyruvate, fatty acids, and leucine. Q. Acetyl CoA is used for what purposes? (Page 195) A. Oxidation in TCA cycle, fatty acid synthesis, cholesterol synthesis, and ketone body formation. Q. Give examples of substrate level phosphorylation. (Page 195) A. 1,3-bisphospho glycerate kinase, pyruvate kinase, and succinate thiokinase.

Citric Acid Cycle

145

Q. Which is the substrate level phosphorylation step in the TCA cycle? A. Succinate thiokinase. (Page 194) Q. What is the inhibitor of succinate dehydrogenase? (Page 197) A. Malonate. Q. Give examples of reactions in which NADH is generated. (Page 197) A. Pyruvate dehydrogenase, isocitrate dehydrogenase, and alpha keto glutarate dehydrogenase. Q. How many ATPs are generated per one rotation of the citric acid cycle? (Page 197) A. 12 ATP. Q. What is the net yield of ATP from one molecule of glucose in anaerobic glycolysis? (Page 79) A. 2 ATP. Q. What is the net yield of ATP from one molecule of glucose in aerobic glycolysis? (Page 79) A. 8 ATP. Q. During complete oxidation, what is the net yield of ATP from one glucose molecule? (Page 79) A. 38 ATP. Q. Which is the amphibolic pathway? A. Citric acid cycle.

(Page 197)

Q. How TCA cycle is regulated? (Page 198) A. Availability of ATP, NAD+ and oxaloacetate.

146 Viva—based on Textbook of Biochemistry Q. Succinyl CoA is formed from which substrates? (Page 199) A. Isoleucine, valine, methionine, andodd chain fatty acids. Q. Fumarate is produced from which substances? (Page 199) A. A. Arginino succinate B. Phenyl alanine. Q. Alpha keto glutaric acid is formed from which substances? (Page 199) A. Glutamic acid, histidine, arginine, and proline. Q. Aspartic acid enters the TCA cycle at which level? (Page 199) A. Oxalo acetate. Q. In normal resting state, most of the glucose is utilised by which tissue? A. Brain. (Page 200) Q. What is the approximate percentage of storage form of energy (total fuel reserve) present in a normal human body? (Page 200) A. Fat 85%, glycogen 1%, protein 14%. Q. During starvation, which substances are increased in blood? (Page 201) A. Ketone bodies, glucagon, and epinephrine.

Electron Transport Chain

147

Electron Transport Chain

Q. Give examples of high energy compounds. (Page 206) A. ATP, GTP, creatine phosphate, 1,3-bis phospho glycerate, phosphoenol pyruvate, acetyl CoA, and succinyl CoA. Q. On hydrolysis of 1 mole of ATP to ADP, the release of energy will be approximately how much? (Page 206) A. 7 kCal. Q. Where is respiratory chain located? (Page 207) A. In the inner mitochondrial membrane. Q. How is respiratory chain organised? (Page 207) A. Components are organised into four complexes. Q. What are the activities taking place inside mitochondria? (Page 207) A. Citric acid cycle, electron transport chain, and beta oxidation fatty acid.

148 Viva—based on Textbook of Biochemistry Q. Where are enzymes of citric acid cycle located? (Page 207) A. Fluid matrix contains enzymes of citric acid cycle. Q. What is the function of Co-enzyme Q? (Page 208) A. It catalyses the electron transport from complex I or II to complex III. Q. Cytochrome oxidase is present in which complex? (Page 209) A. Complex IV. Q. What are NAD+ linked dehydrogenases? (Page 209) A. Glyceraldehyde-3-phosphate dehydrogenase, pyruvate dehydrogenase, alpha keto glutarate dehydrogenase, isocitrate dehydrogenase, malate dehydrogenase, beta hydroxy acyl CoA dehydrogenase. Q. What are FAD-linked dehydrogenases? (Page 209) A. Succinate dehydrogenase, and acyl CoA dehydrogenase. Q. Which cytochromes contain copper? (Page 209) A. Cytochrome oxidase. Q. What is valinomycin? (Page 210) A. It acts as an ionophore, dissipates the proton gradient, and so inhibits ATP synthesis. Q. What is atractylocide? (Page 210) A. It inhibits translocase, and inhibits ATP synthesis.

Electron Transport Chain

149

Q. What are the salient features of ATP synthase? (Page 210) A. It has two subunits, Fo is a proton channel, and F1 has catalytic activity. Q. How many ATP are produced in the oxidation of one molecule of NADH? (Page 210) A. Three. Q. How many ATP are produced in the oxidation of one molecule of FADH? (Page 210) A. Two. Q. Which is complex V of respiratory chain? (Page 210) A. ATP synthase. Q. What is oligomycin? (Page 210) A. It inhibits oxidative phosphorylation. Q. Name some inhibitors of oxidative phosphorylation. (Page 211) A. Oligomycin, carbon monoxide, and cyanide. Q. Which inhibits electron transport chain at site 1? (Page 211) A. Barbiturate. Q. Which inhibits electron transport chain at site 2? (Page 211) A. Naphthoquinone. Q. Which inhibits electron transport chain at site 3? (Page 211) A. Carbon monoxide and cyanide.

150 Viva—based on Textbook of Biochemistry Q. What is the cause for death due to cyanide poisoning? (Page 211) A. Cyanide inhibits cytochrome oxidase. Q. Which is a physiological uncoupler? (Page 211) A. Thyroxine. Q. Which is the inborn error due to a mutation in NADH-Q reductase? A. Leber’s hereditary neuropathy (LHON). (Page 211)

Plasma Proteins Free Radical and Anti-oxidants

151

Free Radicals and Anti-oxidants

Q. Name the free radicals. A. Superoxide anion radical, hydroperoxyl radical, hydrogen peroxide, hydroxyl radical, lipid peroxide radical, singlet oxygen, nitric oxide, and peroxy nitrite. Q. What are the important characteristics of reactive oxygen species? A. Extreme reactivity, short life span, generation of new ROS by chain reaction, and damage to various tissues. Q. What are the enzymes generating ROS in macrophages? A. NADPH oxidase, superoxide dismutase, and myeloperoxidase.

152 Viva—based on Textbook of Biochemistry Q. What are the biological effects of ROS? A. Protein damage, loss of function, lipid peroxidation, membrane damage, mitochondrial damage, DNA damage, cell death, mutation, and cancer. Q. What are the free radical scavinging enzymes? A. Superoxide dismutase, glutathione peroxidase, glutathione reductase, and catalase. Q. ROS causes what diseases? A. Chronic inflammation, rheumatoid arthritis, acute inflammations, bronchopulmonary dysplasia, respiratory distress syndrome, retrolental fibroplasia, cataract, reperfusion injury, atherosclerosis, and peptic ulcer. Q. Name important anti-oxidants. A. Alpha tocopherol (Vitamin E), Vitamin C, Vitamin A, and beta carotene.

Plasma Proteins

153

Plasma Proteins Q. What is normal serum albumin level?(Page 216) A. 3.5-5 mg/dl. Q. What is the normal value of total proteins in serum? (Page 216) A. 6-8 g/100 ml. Q. Edema due to hypoproteinemia is seen in which conditions? (Page 217) A. Cirrhosis liver, malnutrition, and nephrotic syndrome. Q. In blood, albumin carries what substances? (Page 217) A. Free fatty acids, bilirubin, salicylate, and calcium. Q. What is the clinical application of albumin carrying bilirubin? (Page 217) A. Bilirubin and salicylate compete for binding to albumin, and so it is not safe to give salicylate to infants having hemolytic disease.

154 Viva—based on Textbook of Biochemistry Q. What are the functions of albumin? (Page 217) A. It maintains colloidal osmotic pressure of plasma, and it transports non-esterified fatty acid and bilirubin. Q. Albumin is synthesised in which organ? (Page 217) A. Liver. Q. Where is gamma globulins synthesised? (Page 217) A. By reticulo endothelial system (Spleen, lymph nodes). Q. Polymorphism is exhibited by which proteins? (Page 218) A. Haptoglobin, transferrin, and ceruloplasmin. Q. Albumin globulin ratio is reversed in which conditions? (Page 218) A. Cirrhosis, chronic infections, nephrotic syndrome, and multiple myeloma. Q. Name some transport proteins. (Page 218) A. Transthyretin (thyroid hormones), retinol binding protein, thyroxine binding globulin, transcortin (cortisol), haptoglobin (hemoglobin), transferrin (Iron), and hemopexin (free heme). Q. Name acute phase proteins. (Page 219) A. C-reactive protein, ceruloplasmin, and haptoglobin.

Plasma Proteins

155

Q. What is the clinical manifestation of Alpha-1anti-trypsin deficiency? (Page 219) A. Emphysema and chronic lung infections. Q. What is ceruloplasmin? (Page 219) A. It is a copper containing enzyme (ferroxidase) seen in blood. It is an acute phase protein. Q. What is the clinical significance of ceruloplasmin? (Page 219) A. Ceruloplasmin level in blood is decreased in Wilson’s hepatolenticular degeneration. Q. What is the carrier protein of copper? (Page 219) A. Albumin. Q. Hemopexin carries what? A. Free heme.

(Page 220)

Q. How hemophilia is manifested? (Page 222) A. Non-stopping hemorrhage after minor injuries. Q. How hemophilia is transmitted? (Page 222) A. It is inherited as an x-linked recessive trait, males are affected, females are carriers. Q. Hemorrhage tendency is seen in which conditions? (Page 222) A. Hemophilia, Vitamin K deficiency, and thrombocytopenia

156 Viva—based on Textbook of Biochemistry

Immunochemistry

Q. How immunoglobulins are classified? (Page 225) A. IgG, IgM, IgA, IgD and IgE. Q. What is the basic structure of an immunoglobulin? (Page 225) A. Two heavy chains and two light chains connected by disulphide linkages. Q. The antigen binding capacity of immunoglobulin resides at which region of immunoglobulin? (Page 225) A. Variable region. Q. What is primary response antibody? (Page 226) A. Immunoglobulin M. Q. What is the secondary response antibody? (Page 226) A. Immunoglobulin G.

Heme Synthesis Immunochemistry and Breakdown

157

Q. Which antibody is seen in body secretions? (Page 227) A. Immunoglobulin A. Q. What is the clinical importance of immunoglobulin E? (Page 227) A. They mediate anaphylactic reaction. Q. What is the cause of anaphylactic reaction? (Page 227) A. IgE attach on mast cells, when antigen is introduced, antigen antibody reaction occurs, and leading to mast cell degranulation. Q. What is M band? (Page 228) A. A narrow peak in gamma globulin, caused by monoclonal antibodies secreted by malignant plasma cells. Q. What is Bence Jones protein? (Page 228) A. It is the light chains of immunoglobulins, excreted in urine. It is seen in urine of 20% cases of multiple myeloma. Q. What is the test done to detect Bence Jones protein? (Page 228) A. It is precipitated when heated between 45 and 60 degrees. Q. How antibody diversity is produced?(Page 230) A. By somatic recombination.

158 Viva—based on Textbook of Biochemistry

Specialised Proteins: Collagen, Myosin Q. What is the structural arrangement of collagen? (Page 233) A. It has triple stranded quarter staggered arrangement. One-third residues are glycine. About 1% residues are proline and hydroxy proline. Q. What are the post-translational modifications taking place in collagen? A. Hydroxylation of proline and lysine residues, and hydrolysis of pro-collagen. (Page 233) Q. Hydroxylation of proline and lysine needs what? (Page 233) A. It depends on vitamin C. Q. In ascorbic acid deficiency, what happens? (Page 233) A. Poor hydroxylation, defective collagen and scurvy.

Specialised HemeProteins: SynthesisCollagen and Breakdown Myosin

159

Q. Cross links in collagen are formed by what? (Page 234) A. It is formed between lysine and hydroxy lysine residues. It is called desmosine. Q. What is the enzyme for cross linkage formation? (Page 234) A. Lysyl oxidase. Q. What is its clinical application? (Page 234) A. Lysyl oxidase contains copper. So, in copper deficiency lysine cross-link formation is deficient, leading to defective collagen. Q. What are inherited disorders leading to defective collagen formation? A. Osteogenesis imperfecta, Ehlers-Danlos syndrome, dermatoparaxis, homocystinuria, and marfan’s syndrome. (Page 234) Q. What is myosin? (Page 236) A. It is a specialised protein seen in muscle. Q. What is its biological function? (Page 236) A. It can bind actin to form actomyosin. It has ATPase activity. Q. What is the function of Troponin-C ? (Page 237) A. It binds calcium. Q. What is the function of Troponin-I ? (Page 237) A. ATPase inhibitory element. Q. What is the clinical significance of Troponin-T ? (Page 237) A. Its serum level is increased in myocardial infarction.

160 Viva—based on Textbook of Biochemistry

Heme Synthesis and Breakdown Q. What is the chemical structure of heme? (Page 240) A. It is ferro protoporphyrin. Q. What are the substituent groups of heme? (Page 240) A. Methyl, vinyl, and propionyl groups. Q. Heme is synthesised from what substances? (Page 241) A. It is synthesised from glycine and succinyl CoA. Q. What is the rate limiting enzyme of heme synthesis? (Page 241) A. ALA synthase. Q. Which enzyme is inhibited by lead? (Page 241) A. ALA dehydratase and ferrochelatase. Q. Methenyl bridge of protoporphyrin is derived from what? (Page 241) A. Alpha carbon of glycine.

Heme Synthesis and Breakdown

161

Q. How is heme synthesis regulated? (Page 242) A. ALA synthase is repressed by heme, and ALA synthase is allosterically inhibited by hematin. Q. What is the action of barbiturates on heme synthesis? (Page 242) A. Barbiturates will induce heme synthesis. Q. What is the treatment for acute intermittent porphyria? (Page 243) A. High carbohydrate diet, and stoppage of barbiturates. Q. What is the defect in acute intermittent porphyria? (Page 243) A. PBG-deaminase. Q. How porphyrins are detected? (Page 243) A. They show fluorescence under ultra violet light. Q. In acute intermittent porphyria, urine contains what? (Page 243) A. ALA and PBG. Q. Lead poisoning results in elevated levels of what? (Page 244) A. Delta amino levulinic acid. Q. Degradation of heme needs which enzyme? (Page 245) A. Heme oxygenase system, with NADPH. Q. Degradation of heme to bilirubin releases what gas? (Page 245) A. Carbon monoxide.

162 Viva—based on Textbook of Biochemistry Q. Heme is converted to bilirubin in which site? (Page 245) A. Microsomes of reticulo-endothelial cells. Q. Bilirubin in blood is carried by what?(Page 245) A. Albumin. Q. How it is made water soluble? (Page 245) A. By conjugation with glucuronic acid. Q. Where is the conjugation taking place? (Page 245) A. In liver. Q. What is the enzyme? A. UDP-glucuronyl transferase.

(Page 245)

Q. What is the normal level of plasma bilirubin? (Page 246) A. 0.2-0.8 mg/dl. Q. What is the normal level of conjugated bilirubin in plasma? (Page 246) A. Less than 0.2 mg /dl. Q. What is latent jaundice? (Page 246) A. When plasma bilirubin is between 1 to 2 mg/dl. Q. What is jaundice? (Page 246) A. When plasma bilirubin is more than 2 mg/dl, it diffuses into tissues, causing yellowish discolouration of tissues. Q. Enterohepatic circulation is seen in which substances? (Page 246) A. Urobilinogen and bile salts.

Heme Synthesis and Breakdown

163

Q. What is the defect in Gilbert’s disease? (Page 247) A. Uptake of bilirubin by the liver is defective. Q. What is the defect in Criggler-Najjar syndrome? (Page 247) A. Defect in conjugation of bilirubin due to deficiency of UDP glucuronyl transferase. Q. Conjugated hyperbilirubinemia is seen in which condition? (Page 247) A. Dubin Johnson’s syndrome. Q. Bilirubin in serum is estimated by what test? (Page 247) A. Van den Bergh reaction. Q. What is Direct van den Bergh’s reaction? (Page 247) A. The colour is developed immediately when blood is added. Q. What is your inference, when direct test is positive? (Page 247) A. Blood contains conjugated bilirubin, it is water soluble. Q. What is indirect van den Bergh’s test?(Page 247) A. When blood is added to the solution, there is no colour, but when alcohol is added, colour is developed. Q. What is the reason for this type of reaction? (Page 247) A. Bilirubin is soluble in alcohol, and alcohol extract gives the reaction.

164 Viva—based on Textbook of Biochemistry Q. What is kernicterus? (Page 248) A. In young children, when plasma bilirubin is more than 20 mg/dl, it diffuses into brain, causing permanent damage to brain cells. Q. In obstructive jaundice, what is seen in blood? (Page 248) A. Conjugated bilirubin in excess quantity. Q. Bile salts and bile pigments are excreted in urine in which condition? A. Obstructive jaundice. (Page 248) Q. Increased urobilinogen in urine is seen in which conditions? (Page 248) A. Congenital spherocytosis, mismatched transfusion, Rh incompatibility, auto-immune hemolysis, and glucose-6-phosphate dehydrogenase deficiency.

Haemoglobins

165

Haemoglobins

Q. What are the salient structural features of hemoglobin molecule? A. Hb has four subunits, two alpha and two beta units. It contains four iron atoms. Q. How many molecules of oxygen can bind with hemoglobin? A. Hb can bind four molecules of oxygen.(Page 249) Q. 100 ml of blood can carry how much oxygen? (Page 250) A. 20 ml. Q. What is Bohr effect? (Page 251) A. The influence of pH and pCO2 to facilitate oxygenation of Hb in the lungs and deoxygenation at the tissues is known as the Bohr effect. Q. What is chloride shift? (Page 251) A. When CO2 is taken up, chloride ions from the plasma would enter. This is called chloride shift or Hamburger effect.

166 Viva—based on Textbook of Biochemistry Q. Hemoglobin carries how much CO2? (Page 251) A. Seventy five percent as isohydric transport and 15% as carbamino hemoglobin. Q. What are the forms in which carbon dioxide is transported? (Page 251) A. Dissolved form, isohydric transport, and carbamino hemoglobin. Q. What is isohydric transport of carbon dioxide? (Page 251) A. There is minimum change in pH during the transport. Q. How this is effected? (Page 251) A. The H+ ions are buffered by the deoxy-Hb. Q. Which will decrease the affinity of hemoglobin for oxygen? A. 2,3-BPG level. (Page 252) Q. What is the structural difference between HbA and HbF? A. HbA has two alpha and two beta chains, but HbF has two alpha and two gamma chains.(Page 252) Q. What are the laboratory tests to identify HbF? (Page 252) A. HbF moves slower than HbA on electrophoresis, HbF is alkali resistant. Q. What is the physiological significance of HbF? (Page 252) A. Oxygen affinity is more for HbF than HbA. HbF is seen in foetal circulation.

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Q. What is the clinical significance of HbF? (Page 252) A. It is seen in adults in hemoglobinopathies and thalassemias. Q. Why carbon monoxide becomes a poison? (Page 253) A. Hb has more affinity to carbon monoxide than oxygen. Q. What is the treatment for carbon monoxide poison? (Page 253) A. Hyperbaric oxygen. Q. Met-hemoglobin is found in which conditions? (Page 253) A. Ingestion of nitrites, presence of HbM, GPD deficiency. Q. What is met-hemoglobin? (Page 253) A. Hemoglobin in which iron is in ferric state. Q. What is the defect of met-hemoglobin? (Page 253) A. It cannot release oxygen in tissues. Q. What is the reagent used for colourimetric estimation of hemoglobin? (Page 254) A. Drabkin’s reagent, to convert Hb to cyanmethemoglobin. Q. What is hemoglobin S? (Page 254) A. The glutamic acid in the 6th position of beta chain of HbA is changed to valine in HbS.

168 Viva—based on Textbook of Biochemistry Q. What is the cause for sickle cell anemia? A. Solubility of deoxy HbS is lower than deoxy HbA, so HbS is precipitated intracellularly, leading to sickle shape of RBC. Q. How HbS is identified? A. HbS is slower moving on electrophoresis than HbA. Q. What is sickle cell trait? A. Heterozygous (AS) condition, one allele is normal, the other is abnormal, so half of Hb molecules are normal, and half abnormal. Q. What is its clinical significance? A. Sickle cell trait persons will not have any disease manifestations, usually. But, at higher altitudes, hypoxia may cause manifestation of the disease. Chronic lung disorders may also produce hypoxia-induced sickling in HbS trait.

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Vitamin-I:

Fat Soluble Vitamins: A, D, E and K Q. What is the pro-Vitamin for Vitamin A? (Page 259) A. Beta carotene present in plants. Q. What is the major function of Vitamin A? (Page 260) A. In vision, as the Wald’s visual cycle. Q. What causes the nerve impulse in retina? (Page 260) A. Photo-isomerisation of 11-cis retinal to all transretinal. Q. How is all trans-retinal regenerated? (Page 261) A. Trans-retinal is taken to liver, where it is made to trans-retinol, then isomerised to cis-retinol and then to cis retinal. Q. What are the enzymes required for this regeneration? (Page 261) A. Alcohol dehydrogenase and retinol isomerase.

170 Viva—based on Textbook of Biochemistry Q. What are other minor biological roles of Vitamin A? (Page 262) A. Normal maintenance of epithelium and skin, glycoprotein synthesis, reproduction, cell differentiation, and anti-oxidant role. Q. What are the sources of Vitamin A? (Page 262) A. Carrot, mangoes, papaya, green leafy vegetables, and fish liver oil. Q. What are the deficiency manifestations of Vitamin A? (Page 262) A. Night blindness, xerophthalmia, keratomalacia, and keratinisation of epithelium. Q. Nyctalopia is due to the deficiency of which Vitamin? (Page 262) A. Vitamin A. Q. What is the daily requirement of Vitamin A? (Page 263) A. 750 to 1000 microgram. Q. How cholecalciferol is synthesised? (Page 263) A. From 7-dehydro cholesterol in the malpighian layer of epidermis, by the action of ultra violet rays. Q. How Vitamin D is activated? (Page 264) A. Cholecalciferol from skin reaches liver. There it is hydroxylated to form 25-hydroxy cholecalciferol (25-HCC). It then reaches kidney, where further hydroxylation takes place to form 1,25-dihydroxy cholecalciferol (DHCC).

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Q. What is calcitriol? (Page 264) A. 1,25-dihydroxy cholecalciferol, or active Vitamin D, contains three hydroxyl groups at 1, 3 and 25 positions. So it is called calcitriol. Q. Which Vitamin acts as a pro-hormone? (Page 264) A. Vitamin D. Q. What is the function of Vitamin D? (Page 264) A. It increases absorption of calcium from intestine, and it also increases mineralisation of bone. Q. How Vitamin D increases absorption of calcium? (Page 264) A. Calcitriol binds to a cytoplasmic receptor. The hormone-receptor complex interacts with DNA and causes transcription of specific genes that code for calbindin. Due to the increased availability of calcium binding protein, the absorption of calcium is increased. Q. How is Vitamin D deficiency manifested? (Page 265) A. Rickets in children and osteomalacia in adults. Q. In renal disease, oral doses of Vitamin D may not be effective, why? (Page 265) A. Hydroxylation and activation of Vitamin is taking place in kidney. Q. What are the causes of rickets? (Page 265) A. Chronic renal failure, liver diseases, and underexposure to sunlight.

172 Viva—based on Textbook of Biochemistry Q. What is the daily requirement of Vitamin D? (Page 265) A. 5-10 microgram. Q. What is the chemical nature of Vitamin E? (Page 265) A. Alpha tocopherol. Q. What is the function of Vitamin E ? A. Anti-oxidant.

(Page 266)

Q. What is the relationship of selenium with Vitamin E? (Page 266) A. They act synergistically as anti-oxidants. Q. What is the source of Vitamin E? (Page 266) A. Vegetable oils are rich sources of Vitamin E, e.g. wheat germ oil, sunflower oil, safflower oil, cotton seed oil, and palm oil. Q. What is the normal daily requirement of Vitamin E? (Page 266) A. 15 mg or 33 international units. Q. What is the chemical nature of Vitamin K? (Page 266) A. Naphthoquinone derivative. Q. What is menadione? (Page 266) A. It is synthetic water soluble Vitamin K, widely used in clinical practice. Q. What is the function of Vitamin K? (Page 267) A. Gamma carboxylation of clotting factors such as prothrombin.

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Q. Deficiency of Vitamin K can occur in which conditions? (Page 267) A. Obstructive jaundice, antibiotic therapy, and administration of dicoumarol. Q. What is the mechanism of action of dicoumarol? (Page 267) A. It competitively inhibits Vitamin K epoxide reductase. Q. So, dicoumarol is used for what purpose? (Page 267) A. To prevent intravascular thrombosis. Q. Excess dicoumarol will produce what?(Page 267) A. Bleeding tendency. Q. Which substance will inhibit Vitamin K? (Page 267) A. Dicoumarol. Q. Excess dose of Vitamin K in neonates may lead to which condition? A. Hemolysis and jaundice. (Page 267) Q. Bleeding tendency is common in the deficiency of which? (Page 267) A. Vitamin K, Vitamin C, and platelets.

174 Viva—based on Textbook of Biochemistry

Vitamin-II:

Water soluble vitamins

Q. What is the source of thiamine? (Page 268) A. Aleurone layer of cereals (food grains) is a rich source of thiamine. Whole wheat flour and unpolished rice and yeast are very good sources. Q. Thiamine pyrophosphate is required for which reactions ? (Page 268) A. Transketolase, pyruvate dehydrogenase, and alpha keto glutarate dehydrogenase. Q. Which Vitamin is required for oxidative decarboxylation? (Page 268) A. Thiamine pyrophosphate. Q. In thiamine deficiency, what alterations are seen in blood ? (Page 269) A. Increased pyruvic acid level and increased transketolase activity.

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Q. What are the clinical manifestations of thiamine deficiency? (Page 269) A. Beriberi, Wernick’s syndrome, and polyneuritis. Q. Beberi is due to the deficiency of which Vitamin? (Page 269) A. Thiamine. Q. What is the daily requirement of Vitamin B1 (thiamine) ? (Page 269) A. 1 to 1.5 milligram. Q. Chronic alcoholism may lead to the deficiency of which Vitamin? A. Vitamin B1. (Page 269) Q. Wernicke’s encephalopathy is due to the deficiency of which Vitamin? A. Vitamin B1. (Page 269) Q. What is the co-enzyme function of riboflavin ? (Page 269) A. FMN and FAD dependent enzymes. Q. What are the FAD dependent enzymes? (Page 270) A. Succinate dehydrogenase, acyl CoA dehydrogenase, xanthine oxidase, glutathione reductase, glycine cleavage system, pyruvate dehydrogenase, and alpha ketoglutarate dehydrogenase. Q. What are the manifestations of riboflavin deficiency? (Page 270) A. Glossitis, cheilosis, angular stomatits, and circumcorneal vascularisation.

176 Viva—based on Textbook of Biochemistry Q. What is the dietary sources of riboflavin? (Page 270) A. Rich sources are liver, dried yeast, egg, and milk. Q. What is the daily requirement of riboflavin? (Page 270) A. 1.5 mg per day. Q. Which Vitamin is synthesised in the body? (Page 271) A. Niacin. Q. What is the co-enzyme function of niacin? (Page 271) A. NAD and NADP. Q. Name some important NAD dependent enzymes. (Page 271) A. Lactate dehydrogenase, glyceraldehyde-3phosphate dehydrogenase, pyruvate dehydrogenase, beta hydroxy acyl CoA dehydrogenase, and mitochondrial isocitrate dehydrogenase. Q. Name the NADPH generating reactions. (Page 271) A. Glucose-6-phosphate dehydrogenase, 6-phospho gluconate dehydrogenase, malic enzyme, and cytoplasmic isocitrate dehydrogenase. Q. What are the important NADPH utilising reactions? (Page 271) A. Beta keto acyl ACP dehydrogenase, alpha, beta unsaturated ACP dehydrogenase, HMGCoA reductase, met-hemoglobin reductase, dihydrofolate reductase, and phenylalanine hydroxylase.

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Q. Pellagra is seen in the deficiency of which Vitamin? (Page 271) A. Niacin. Q. What are the features of pellagra ? A. Dermatitis, diarrhea, and dementia.

(Page 271)

Q. What is the precursor of niacin? A. Tryptophan.

(Page 271)

Q. Tryptophan will give rise to how much niacin? (Page 272) A. About 60 mg of tryptophan will yield 1 mg of niacin. Q. Tryptophan is deficient in which food stuff? (Page 272) A. Maize and corn. Q. Which conditions will lead to symptoms of pellagra? (Page 272) A. Isoniazid therapy, low tryptophan content in diet, niacin deficiency, hartnup disease, and carcinoid syndrome. Q. What is the dietary sources of niacin?(Page 272) A. Natural sources of niacin are dried yeast, rice polishing, liver, peanut, whole cereals, legumes, meat and fish. About half of the requirement is met by the conversion of tryptophan to niacin. About 60 mg of tryptophan will yield 1 mg of niacin. Q. What is the daily requirement of niacin? (Page 272) A. The R.D.A is 20 mg/day.

178 Viva—based on Textbook of Biochemistry Q. Transamination reaction requires which Vitamin? (Page 272) A. Pyridoxal phosphate. Q. Pyridoxal phosphate is required for what reactions? (Page 272) A. Transamination reactions, decarboxylation of amino acids, ALA synthase, glycogen phosphorylase. Q. Give an example of transamination reaction. (Page 272) A. Alanine transaminase (ALT) will catalyse the reaction, alanine to pyruvate. Q. What is its clinical significance? A. Blood level of ALT is increased in liver diseases, AST is increased in myocardial infarction. Q. Give some examples of decarboxylation reactions. (Page 273) A. Glutamate to GABA (gamma aminobutyric acid), histidine to histamine, 5-hydroxy tryptophan to serotonin, cysteine to taurine, and serine to ethanol amine. Q. Xanthurenic acid in urine is seen in the deficiency of which Vitamin? A. Pyridoxal deficiency. (Page 273) Q. What are the manifestations of pyridoxal deficiency? (Page 273) A. Infantile convulsions, peripheral neuritis, pellagra, and anemia.

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Q. What is the reason for infantile convulsions in pyridoxal deficiency? A. Pyridoxal phosphate is required for the formation of GABA, and it is an inhibitory neurotransmitter, absence of which leads to hyper-excitation and convulsions. (Page 273) Q. What is the reason for peripheral neuritis in pyridoxal deficiency? A. PLP is involved in the synthesis of sphingolipids, so B6 deficiency leads to demyelination of nerves and consequent peripheral neuritis. (Page 273) Q. What is the reason for pellagra-like disease in pyridoxal deficiency? A. Since niacin is produced from tryptophan, one of the enzymes of this pathway is PLP dependent. So B6 deficiency in turn leads to niacin deficiency which is manifested as pellagra. (Page 273) Q. Can you give an exmple of one Vitamin deficiency leading to another Vitamin deficiency? (Page 273) A. PLP deficiency in turn leads to niacin deficiency which is manifested as pellagra. Q. What is the reason for anemia in pyridoxal deficiency? (Page 273) A. PLP is required for ALA synthase. In adults hypochromic microcytic anemia may occur due to the inhibition of heme biosynthesis.

180 Viva—based on Textbook of Biochemistry Q. What are the drugs which cause pyridoxal deficiency? (Page 274) A. Isonicotinic acid hydrazide (INH) (isoniazid), cycloserine, penicillamine and oral contraceptives act as B6 antagonists. Ethanol in the body is converted to acetaldehyde, which inactivates PLP. Q. What are the dietary sources of pyridoxal? (Page 274) A. Rich sources are yeast, rice polishing, wheat germs, cereals, legumes (pulses), egg, milk, meat, fish and green leafy vegetables. Q. What is the daily requirement of pyridoxal phosphate? (Page 274) A. 1 to 2 mg/day. Q. What is the co-enzyme form of pantothenic acid? (Page 274) A. Co-enzyme A. Q. What is the function of CoA? (Page 274) A. Oxidation of pyruvic acid and activation of acyl groups. Q. Deficiency of pantothenic acid leads to what? (Page 274) A. Burning foot syndrome. Q. What are the donors for acetyl CoA pool? (Page 275) A. Pyruvate, fatty acid, and amino acids.

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Q. Acetyl CoA is used for what purposes? (Page 275) A. Oxidation in TCA cycle, fatty acid synthesis, cholesterol synthesis, steroid synthesis, and ketone body formation. Q. Succinyl CoA is used for what purposes? (Page 275) A. Oxidation in TCA cycle, heme synthesis, and activation of acetoacetate. Q. What is the function of biotin? A. Carboxylation reactions.

(Page 275)

Q. Name some reactions dependent on biotin. (Page 275) A. Acetyl CoA carboxylase, propionyl CoA carboxylase, and pyruvate carboxylase. Q. What is the antagonist for biotin? A. Avidin.

(Page 276)

Q. What is its use in laboratory? (Page 276) A. Biotin-avidin reaction is used in immunosorbent assays. Q. What is the chemical nature of folic acid? (Page 276) A. Pteroyl glutamic acid (pteridine + PABA + glutamic acid). Q. What is PABA? A. Para amino benzoic acid.

(Page 276)

182 Viva—based on Textbook of Biochemistry Q. What is the co-enzyme form of folic acid? (Page 276) A. Tetrahydro folic acid. Q. What is the main function of folic acid? (Page 276) A. Tetrahydro folic acid is the carrier of one carbon units. Q. What are the causes of folate deficiency? (Page 277) A. Pregnancy, defective absorption (sprue, celiac disease), anticonvulsant drugs (hydantoin, dilantin, phenytoin, phenobarbitone), hemolytic anemias, and dietary deficiency. Q. What is the major manifestation of folic acid deficiency? A. Macrocytic anemia. (Page 277) Q. Folic acid deficiency in pregnancy is associated with what? (Page 277) A. Folic acid deficiency during pregnancy may lead to neural tube defects in the fetus. Folic acid prevents birth defects (fetal malformations such as spina bifida). Q. What are the other minor effects of folic acid? (Page 277) A. Folic acid is also useful to reduce the level of homo-cysteine in blood, and therefore helps in preventing heart diseases. Folic acid is beneficial in prevention of cancer.

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Q. What are the laboratory findings in folic acid deficiency? (Page 278) A. (1) Normal folic acid level in serum is decreased. (2) FIGLU is excretion is more, especially after histidine load. (3) AICAR excretion in urine. (4) Peripheral blood picture shows macrocytic anemia. (5) Homocysteine level in blood is increased Q. What are the sources of folic acid? (Page 278) A. Yeast, liver, egg, green leafy vegetables, cereals, and pulses. Q. What is the daily requirement of folic acid? (Page 278) A. The RDA of free folate is 200 mg/day. In pregnancy the requirement is increased to 400 mg/day. Q. What is the mechanism of action of sulphonamides? (Page 278) A. They are anti-bacterial agents. They have structural similarity with PABA. Therefore they competitively inhibit the enzyme responsible for the incorporation of PABA into folic acid. Q. What is the mechanism of action of trimethoprim? (Page 278) A. It inhibits the folate reductase and so formation of THFA is reduced. It is bactericidal agent. Q. What is mechanism of action of methotrexate? (Page 278) A. It inhibits folate reductase, and is a powerful anticancer drug. Q. What are inhibitors of folic acid? (Page 278) A. Methotrexate, trimethoprim, pyrimethamine and sulphonamide.

184 Viva—based on Textbook of Biochemistry Q. Name a water soluble Vitamin, which is stored in the body. A. Vitamin B12. (Page 279) Q. What is the metal present in Vitamin B12? (Page 279) A. Cobalt. Q. What is the ring system present in Vitamin B 12? (Page 279) A. Corrin ring. Q. Vitamin B12 is absorbed from where?(Page 279) A. Ileum. Q. What is the transport form of Vitamin B12? (Page 279) A. Methyl B 12. Q. What is the carrier of Vitamin B12 in blood? (Page 279) A. Transcobalamin-II, a glycoprotein, is the specific carrier. Q. What is the storage form of Vitamin B12? (Page 279) A. It is stored in the liver cells, as ado-B12 form, in combination with transcobalamin-I or transcorrin. Q. What is the co-enzyme function of Vitamin B 12? (Page 279) A. Methyl malonyl CoA isomerase, and homocysteine methyl transferase.

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Q. What abnormalities are seen in Vitamin B 12 deficiency? (Page 280) A. Methyl malonic aciduria, accumulation of methyl malonic acid, breakdown of myelin sheaths and interruption in nerve transmission. Homocysteinuria is also seen. Q. What abnormal compound is excreted in Vitamin B12 deficiency? A. Methyl malonic acid in urine. (Page 280) Q. What is folate trap? (Page 280) A. The production of methyl THFA is an irreversible step. Therefore, the only way for generation of free THFA is methyl THFA to THFA, by a Vitamin B12 dependent step. When B12 is deficient, this reaction cannot take place. This is called the methyl folate trap. Q. What is the clinical importance of folate trap? (Page 280) A. This leads to the associated folic acid scarcity in B12 deficiency. Q. What is the explanation of demyelination in Vitamin B12 deficiency? A. In Vitamin B12 deficiency, there is non-availability of active methionine. Therefore, methylation of phosphatidyl ethanolamine to phosphatidyl choline is not adequate. This leads to deficient formation of myelin sheaths of nerves. (Page 280)

186 Viva—based on Textbook of Biochemistry Q. What are the causes of B12 deficiency? (Page 280) A. Nutritional B12 deficiency, decrease in absorption, addisonian pernicious anemia, atrophy of gastric epithelium, and pregnancy. Q. What is the cause for pernicious anemia? (Page 280) A. It is an autoimmune disease with a strong familial background. Antibodies are generated against intrinsic factor. So IF is deficient, leading to defective absorption of B12. Q. What are the manifestations of Vitamin B12 deficiency? (Page 280) A. Megaloblastic anemia and subacute combined degeneration. Q. What is the difference in folate deficiency and B12 deficiency? A. In folate deficiency, there is macrocytic anemia, and in B12 deficiency, there is additional neurological symptoms also. (Page 280) Q. What is the daily requirement of Vitamin B12? (Page 280) A. One to two microgram/per day. Q. A patient who has undergone gastrectomy is likely to develop deficiency of which Vitamin? (Page 280) A. Vitamin B12.

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Q. In Vitamin B12 deficiency, what are the abnormalities seen in urine? A. Urine may contain methyl malonic acid, homocystine, cystathione, and formimino glutamic acid. (Page 280) Q. Which is the Vitamin totally absent in plant sources? A. Vitamin B12. (Page 281) Q. What are the sources of Vitamin B12?(Page 280) A. Liver, meat, fish, and curd. Q. What is the chemical structure of Vitamin C? (Page 282) A. L-ascorbic acid. Q. How it is synthesised? (Page 282) A. Man and primates cannot synthesise ascorbic acids. Lower animals could synthesise it from glucose through glucuronic acid pathway. Q. What are the major functions of ascorbic acid? (Page 282) A. Ascorbic acid promotes collagen formation through its action on post-translational hydroxylation of proline and lysine residues. Q. What are the other functions of ascorbic acid? (Page 282) A. Parahydroxy phenyl pyruvate oxidation to homogentisic acid, iron absorption from the intestine, reconversion of methemoglobin to hemoglobin, and adrenal steroidogenesis.

188 Viva—based on Textbook of Biochemistry Q. Which Vitamin is required for post-translational modifications? A. Ascorbic acid. (Page 282) Q. What is the daily requirement of ascorbic acid? (Page 283) A. 75 mg per day. Q. Scurvy is due to the deficiency of which Vitamin? (Page 283) A. Ascorbic acid. Q. What are the important features of scurvy? (Page 283) A. Hemorrhagic tendency, microcytic anemia, bone pain, bleeding gums.

Mineral Metabolism

189

Mineral Metabolism Q. What influences absorption of calcium from intestine? (Page 284) A. Vitamin D, calcitriol, parathyroid hormone, phytic acid, and oxalate. Q. What is the daily requirement of calcium? (Page 284) A. 500 mg per day. Q. What are the sources of calcium? A. Milk, egg, fish, and vegetables.

(Page 284)

Q. What is the function of calcium ? (Page 285) A. Coagulation, neuromuscular activity, intracellular messenger, activation of enzymes, and bone formation. Q. What is the normal level of calcium in blood? (Page 285) A. 9-11 mg /dl.

190 Viva—based on Textbook of Biochemistry Q. Which will influence serum calcium level? (Page 285) A. Calcitriol, calcitonin, and parathyroid hormone. Q. How parathyroid hormone regulates calcium level in blood? A. Bone resorption, increased absorption of calcium from intestines, and increased absorption of calcium from renal tubules. (Page 286) Q. Hypocalcemia results in what clinical condition? (Page 287) A. Tetany. Q. What is the reason for tetany? A. Hypoparathyroidism.

(Page 287)

Q. What are the features of hyperparathyroidism ? (Page 287) A. Osteoporosis, hypercalciuria, and urinary calculi. Q. What is the normal level of phosphorus in blood. (Page 287) A. 3-4 mg /dl. Q. What is the normal level of sodium in blood ? (Page 289) A. 136-145 mEq/L. Q. What is the important extracellular cation? (Page 289) A. Sodium. Q. Which will control the sodium level in serum? (Page 289) A. ADH, aldosterone, and cortisone.

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Q. What is the normal level of potassium in blood ? (Page 289) A. 3.5 to 5 mEq /L. Q. What is the major intracellular cation?(Page 289) A. Potassium. Q. What is the manifestation of hypokalemia? (Page 289) A. In ECG, T wave inverted, ST segment is lowered. Q. What is the normal level of chloride in blood ? (Page 290) A. 96- 106 mEq /L. Q. What is the daily requirement of iron for a normal adult male ? A. 10-20 milligram per day. (Page 291) Q. What are the dietary sources of iron ? (Page 291) A. Green leafy vegetables, meat, and jaggery. Q. Which is the trace element, deficient in milk? (Page 291) A. Iron. Q. What are important iron containing proteins? (Page 291) A. Hemoglobin, myoglobin, cytochromes, catalase, tryptophan pyrrolase, xanthine oxidase, transferrin, and ferritin. Q. Which will increase iron absorption from intestines? (Page 291) A. Gastric HCl, ascrobic acid, and cysteine.

192 Viva—based on Textbook of Biochemistry Q. What are the factors which will retard iron absorption? (Page 291) A. Phytic acid (in cereals) oxalic acid (in leafy vegetables), calcium, zinc, lead and phosphates. Q. Iron is absorbed from which part? A. Upper part of duodenum.

(Page 292)

Q. How is iron absorbed? (Page 292) A. Iron in the intestinal lumen enters the mucosal cell in the ferrous state. This is bound to transferrin molecule present in brush border surface of intestinal cell. One transferrin molecule can bind with two atoms of iron. This is then complexed with a specific receptor. This iron-transferrinreceptor is internalised. Q. How iron absorption is regulated? (Page 292) A. Iron metabolism is unique because homeostasis is maintained by regulation at the level of absorption and not by excretion. When iron stores in the body are depleted, absorption is enhanced. When adequate quantity of iron is stored, absorption is decreased. This is referred to as “mucosal block” of regulation of absorption of iron. Q. What is the carrier protein in iron in blood? (Page 292) A. Transferrin. Q. Which enzyme will help in iron carriage in blood? (Page 292) A. Ferroxidase (ceruloplasmin).

Mineral Metabolism

Q. What is the storage form of iron? A. Ferritin.

193

(Page 293)

Q. What is hemosiderin? (Page 293) A. Excess iron is loaded as hemosiderin. Q. What is haptoglobin? A. It is the carrier of free hemoglobin.

(Page 293)

Q. What is hemopexin? A. It is the carrier of free heme.

(Page 293)

Q. Anemia is resulted in the deficiency of which substances? (Page 293) A. Iron, copper, vitamin C, folic acid, vitamin B12, and pyridoxal phosphate. Q. Iron deficiency results in what? A. Microcytic hypochromic anemia.

(Page 294)

Q. What are the features of hemosiderosis? (Page 294) A. Cirrhosis of liver, diabetes mellitus, and yellow colour of skin. Q. What is the cause for hemosiderosis? (Page 294) A. Repeated transfusion of whole blood. Q. What are the important copper containing enzymes? (Page 294) A. Ceruloplasmin, cytochrome oxidase, cytochrome C, tyrosinase, lysyl oxidae, and super oxide dismutase. Q. What are dietary sources of copper? (Page 294) A. Cereals, meat, and liver.

194 Viva—based on Textbook of Biochemistry Q. What is ceruloplasmin? (Page 294) A. It is ferroxidase, and it promotes oxidation of ferrous ion to ferric form. Q. What are the characteristic features of Wilson’s hepatolenticular degeneration? (Page 295) A. Ceruloplasmin level in blood is decreased, copper excretion is reduced, and copper is accumulated in liver to produce cirrhosis. Q. What is the daily requirement of iodine? (Page 295) A. 150-200 microgram. Q. What is the daily requirement of zinc? (Page 296) A. 15-20 milligram. Q. What are the important enzymes which contain zinc? (Page 296) A. Alkaline phosphatase, amylase, carbonic anhydrase, and RNA polymerase. Zinc is required for insulin secretion. Q. What is Fluorosis? (Page 297) A. It is produced when fluoride concentration in water is more than 20 ppm. Osteoporosis is the manifestation. Q. What is the importance of selenium? (Page 298) A. It is an anti-oxidant. Q. Name the selenium containing enzyme. (Page 298) A. Glutathione peroxidase.

Energy Metabolism and Nutrition

195

Energy Metabolism and Nutrition Q. What is the calorific value of carbohydrates? (Page 299) A. Four kilocalories per gram. Q. What is the calorific value of fats?

(Page 299)

A. Nine kilocalories per gram. Q. How much calories are generated per gram of fat ? (Page 299) A. kCal. Q. What is the respiratory quotient? (Page 299) A. It is the ratio of carbon dioxide produced to the oxygen consumed. Q. What is the respiratory quotient of carbohydrates? (Page 299) A. One.

196 Viva—based on Textbook of Biochemistry Q. What is the respiratory quotient for a mixed diet? (Page 299) A. About 0.82. Q. What is specific dynamic action? (Page 300) A. Increased heat production after intake of food. Q. Which foodstuff has maximum specific dynamic action ? A. Proteins. (Page 300) Q. Basal metabolic rate is increased in which conditions? (Page 300) A. Fever, starvation, cold climate, and increased thyroid hormones. Q. Increased basal metabolic rate is observed in which clinical condition? A. Grave’s disease (hyperthyroidism). (Page 300) Q. What are the beneficial effects of dietary fibre? (Page 301) A. Increased motility of intestine, decreased absorption of cholesterol, and increased glucose tolerance. Q. Name an undigestible carbohydrate. (Page 301) A. Pectin. Q. Which food stuffs contain polyunsaturated fatty acids? (Page 302) A. Vegetable oils, sunflower oil, and groundnut oil. Q. Name essential fatty acids. (Page 302) A. Linoleic acid, linolenic acid, and arachidonic acid.

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Q. What is the dietary advice for a patient with hypercholesterolemia? A. They should take polyunsaturated fatty acids. (Page 302) Q. What foodstuffs contain cholesterol? (Page 302) A. Egg, butter, ghee, and pig fat. Q. A patient with coronary artery disease is advised to refrain from what? A. Egg. (Page 302) Q. What is the recommended daily allowance of protein of a normal adult? (Page 303) A. 1 g/kg. Q. Negative nitrogen balance is observed in which conditions? A. Chronic infection, old age, and malnutrition. (Page 303) Q. Positive nitrogen balance is observed in which conditions? A. Pregnancy, convalescence, and growth period. (Page 303) Q. Lysine is deficient in which foodstuff? (Page 305) A. Pulses. Q. Phenyl alanine is deficient in which food stuff? (Page 305) A. Tapioca. Q. Methionine is deficient in which food stuff? (Page 305) A. Cereals.

198 Viva—based on Textbook of Biochemistry Q. How all amino acids are made available in a mixed diet? A. Supplementation by combining cereals and pulses. (Page 305) Q. What are the salient features of Kwashiorkor? (Page 305, 306) A. Hypoalbuminemia, hypomagnesemia, growth retardation, lethargy, and loss of appetite. Q. How much energy is required for a 60 kg person, with sedentary work? A. 2000 kCal. (Page 307) Q. A balanced diet should have calories for carbohydrate, proteins and fats in which ratio? (Page 307) A. 60:20:20.

Detoxification and Biotransformation of Xenobioticsn Acid Base Balance and pH

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Detoxification and Biotransformation of Xenobiotics Q. What is detoxification process? (Page 310) A. Biochemical processes whereby noxious substances are rendered less harmful or more water soluble and easily excretable. Q. What are xenobiotics? (Page 310) A. They are compounds accidentally ingested or taken as drugs or compounds produced in the body by bacterial metabolism. Q. Give an example of a substance detoxified by reduction. (Page 311) A. Para nitro phenol. Q. Give examples of substances detoxified by hydrolysis. (Page 311) A. Acetanilide to aniline + acetate, aspirin to salicylic acid + acetate.

200 Viva—based on Textbook of Biochemistry Q. Give names of conjugating agents. (Page 311) A. PAPS, UDP glucuronic acid, glutathione, and glycine. Q. Give some examples of substances detoxified by conjugation. A. Bilirubin to bilirubin glucuronide, phenol to phenyl sulfate, and benzoic acid to hippuric acid. (Page 311) Q. Which amino acids are used for detoxification? (Page 311) A. Glutamine, glycine, and cysteine. Q. Give examples of substances detoxified by sulfation. (Page 311) A. Phenol to phenyl sulfate, and indole to indoxyl sulfate. Q. What is the sulfating agent? (Page 311) A. PAPS (phospho adenosyl phospho sulfate). Q. How benzoic acid is detoxified? (Page 311) A. Benzoic acid + glycine = benzoyl glycine or hippuric acid. Q. How epinephrine is excreted? A. As methyl conjugates.

(Page 312)

Q. What is the methylating agent? A. S-adenosyl methionine.

(Page 312)

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Biochemical Aspects of Environmental Pollution Q. What is the most common environmental poison? (Page 314) A. Lead. Q. What are common causes of lead poisoning? (Page 314) A. Paint, lead containig petrol, lead pipes, newspapers, xerox copies and cigarette smoke are important contaminants. Q. What are the occupations in which persons are prone to get lead poisoning? (Page 314) A. Battery repair, radiator repair, soldering, painting and printing. Q. What is the toxic level of lead? (Page 314) A. Blood level of lead, more than 10 ?g/dl in children and more than 25 ?g/dl in adults lead to toxic manifestations.

202 Viva—based on Textbook of Biochemistry Q. What are the manifestations of chronic lead poisoning? (Page 314) A. Miscarriage, stillbirth, and premature birth. In children, mental retardation, learning disabilities, behavioral problems, hyperexcitability and seizures are seen. Anemia, abdominal colic and loss of appetite are very common. Q. What are the manifestation of acute lead poisoning? (Page 314) A. Encephalopathy, convulsions, mania, neuropathy, abdominal colic, severe anemia and kidney damage, discolouration and blue line along the gums. Q. When does acute toxicity is manifested? (Page 314) A. If the blood level of lead is more than 70 mg/dl, acute toxicity is manifested. Q. What is the cause of anemia in lead poisoning? (Page 314) A. Lead inhibits delta amino levulinic acid (ALA) synthase, ALA-dehydratase and ferrochelatase. So, heme synthesis is blocked. Life span of RBC is shortened. Anemia enhances lead absorption, lead in turn produces more anemia, thus a vicious cycle is operating. Q. What are the antidotes for lead poisoning? (Page 314) A. Calcium dodecyl edetate (Calcium disodium versenate), penicillamine and dimercaprol (BAL) are used as antidotes. Dimercaptosuccinic acid is a better but costly antidote.

Acid Base Balance and pH

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Acid Base Balance and pH Q. What is the pH of 0.1 M hydrochloric acid? (Page 319) A. One. Q. When pH falls by 1 unit, what is the change in the hydrogen ion concentration? (Page 319) A. Increases by 10 times. Q. Relationship between pH and pK is given by which equation? (Page 320) A. Henderson-Hasselbalch’s equation. Q. What determines the pH of buffer? A. By the ratio of salt to acid.

(Page 320)

Q. Buffer is most effective when? (Page 320) A. When pK of the acid is nearer to pH. Q. When is the buffering capacity is more? (Page 320) A. When the absolute concentrations of salt and acid are more.

204 Viva—based on Textbook of Biochemistry Q. In the blood, which buffer is most effective? (Page 321) A. Bicarbonate buffer. Q. What are the mechanisms for maintaining the normal pH of plasma? (Page 321) A. Buffers of plasma, lung mechanism, and kidney mechanism. Q. What is the alkali reserve of the body? (Page 321) A. Bicarbonate is the alkali reserve. Q. What is the ratio of bicarbonate to carbonic acid in blood? (Page 321) A. Bicarbonate to carbonic acid ratio is 20. Q. What are the mechanisms by which renal regulation of acid load is achieved? (Page 323) A. Excretion of hydrogen ions in urine, excretion of ammonium ions in urine, and production of bicarbonate in renal tubules. Q. Glutaminase enzyme is used for what purpose? (Page 323) A. For production of ammonia in kidney tubules. Q. What is metabolic acidosis? A. Primary deficit of bicarbonate.

(Page 325)

Q. What are the causes of metabolic acidosis? (Page 326) A. Diabetic ketosis, chronic renal failure, and diarrhea.

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Q. What are the features of diabetic ketoacidosis? (Page 326) A. Lowered bicarbonate, elevated plasma chloride, and increased anion gap. Q. What is the formula used to calculate anion gap? (Page 326) A. (sodium + potassium) minus (chloride + bicarbonate). Q. What is the cause for high anion gap acidosis? (Page 326) A. Diabetic ketoacidosis, chronic renal failure, renal tubular acidosis, lactic acidosis. Q. What is metabolic alkalosis? A. Primary excess of bicarbonate.

(Page 326)

Q. What are the causes of metabolic alkalosis? (Page 326) A. Prolonged vomiting, gastric aspiration, and ingestion of antacids. Q. What is respiratory acidosis? A. Primary excess of carbonic acid.

(Page 326)

Q. What are the causes of respiratory acidosis? (Page 327) A. Bronchial asthma, bronchopneumonia, and narcotic poisoning. Q. What is respiratory alkalosis? A. Primary deficit of carbonic acid.

(Page 327)

206 Viva—based on Textbook of Biochemistry Q. What is the cause for respiratory alkalosis? (Page 327) A. Hyperventillation. Q. What are the results of prolonged vomiting? (Page 327) A. Alkalosis, hypochloremia, and hypokalemia.

ElectrolyteMolecular and WaterBiology BalanceI

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Electrolyte and Water Balance Q. What is the major intracellular cation?(Page 329) A. Potassium. Q. What is the major extracellular cation?(Page 329) A. Sodium. Q. What is the function of anti diuretic hormone? (Page 330) A. Its secretion is stimulated when plasma osmolarity increases, ADH decreases the urine output, and retains water in the body. Q. What are the factors regulating fluid and electrolyte balance? A. Aldosterone and anti diuretic hormone. (Page 330) Q. What are the diuretic drugs used? (Page 330) A. Aldosterone antagonists, angiotensin converting enzyme inhibitors, and carbonic anhydrase inhibitors.

208 Viva—based on Textbook of Biochemistry Q. What is the major cause for isotonic contraction of ECF? (Page 331) A. Small intestinal obstruction. Q. What are the causes for hypotonic contraction of ECF? (Page 331) A. Infusion of dextrose (without saline), Addison’s disease. Q. What are the causes for hypertonic contraction of ECF? (Page 331) A. Diarrhoea, vomiting. Q. What are the causes for isotonic expansion of extracellular fluid? A. Congestive cardiac failure and hyperaldosteronism. (Page 331) Q. What is the cause for hypotonic expansion of extracellular fluid? A. Inappropriate secretion of ADH. (Page 331) Q. What is the important cause for hypertonic expansion of ECF? A. Cushing’s syndrome. (Page 331) Q. What are the metabolic imbalances seen in diarrhea? (Page 331) A. Metabolic acidosis, hypertonic contraction of ECF, urine with high specific gravity, and urine output reduced.

Molecular Biology I

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Molecular Biology-I: Nucleotides, Chemistry and Metabolism

Q. What is a nucleotide? (Page 332) A. Nitrogenous base + sugar + phosphate. Q. What is a nucleoside? A. Nitrogenous base + sugar.

(Page 332)

Q. What are the sugars? (Page 332) A. Ribose in RNA and deoxyribose in DNA. Q. What are the bases present in nucleotides? (Page 332) A. Purines and pyrimidines. Q. Name the common purines. A. Adenine and guanine.

(Page 332)

Q. Name the common pyrimidines. A. Cytosine, uracil, and thymine.

(Page 332)

210 Viva—based on Textbook of Biochemistry Q. What are the bases present in DNA? (Page 332) A. Adenine, guanine, cytosine, and thymine. Q. Which nitrogenous base is absent in DNA? (Page 332) A. Uracil. Q. Which base is found exclusively in DNA and not in RNA? (Page 332) A. Thymine. Q. Which base is found exclusively in RNA and not in DNA? (Page 332) A. Uracil. Q. Which amino acid is required for both purine and pyrimidine synthesis? (Page 333) A. Aspartic acid and glutamine. Q. N3 of purine ring is donated by what?(Page 335) A. Glutamine. Q. Glycine donates what part of the purine ring? (Page 335) A. C4, C5, N7 atoms. Q. N1 atom of purine ring is coming from what? (Page 335) A. Aspartic acid. Q. One carbon pool donates which carbon atoms of purine ring? A. C2 and C8 carbon atoms. (Page 335)

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Q. What is the key enzyme of de novo synthesis pathway of purines? (Page 337) A. The committed step in de novo synthesis is the reaction catalysed by amidotransferase (step 1). Q. How is de novo synthesis of purine regulated? (Page 337) A. Amidotransferase enzyme is inhibited by AMP and GMP. Q. What are the enzymes needed for salvage pathway of purines? (Page 337) A. Adenine phospho ribosyl transferase (APRTase) and hypoxanthine guanine phospho ribosyl transferase (HGPRTase). Q. What is the importance of the salvage pathway? (Page 337) A. This is of special importance in tissues like RBCs and brain where the de novo pathway is not operating. Q. What is the clinical significance of the purine analogues? (Page 338) A. They act as cell cycle inhibitors and can be used as anti-cancer drugs. Q. Give a few examples of purine analogues, used as anti-cancer drugs. (Page 338) A. 6-mercapto-purine inhibits the conversion of IMP to GMP and AMP. 2. Cytosine arabinoside. 3. Folate antagonists (Methotrexate) would affect the reactions involving one carbon group transfers. 4. Azaserine is a glutamine antagonist and therefore inhibits reactions involving glutamine.

212 Viva—based on Textbook of Biochemistry Q. What is the end product of catabolism of purines in human beings? A. Uric acid. (Page 338) Q. What is xanthine oxidase? (Page 338) A. It is the enzyme for the reactions, hypoxanthine to xanthine and xanthine to uric acid. Q. What is the speciality in this reaction?(Page 338) A. Xanthine oxidase is a metalloflavoprotein containing FAD, molybdenum and iron. As xanthine is oxidised to uric acid, hydrogen peroxide (reactive oxygen species) is produced. Q. What is the normal uric acid level in blood? (Page 338) A. The normal blood level of uric acid ranges from 2-5 mg/dl in females and 3-7 mg/dl in males. Q. What is the normal excretion rate of uric acid? (Page 338) A. The daily excretion of uric acid varies from 500700 mg. Q. Which property of uric acid is responsible for the manifestations of gout? (Page 338) A. Uric acid is sparing soluble in water. Q. Increased uric acid level is seen in which conditions? (Page 339) A. Gout, pre-eclampsia, Hodgkin’s lymphoma, leukemia, and diabetic ketoacidosis.

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Q. Hyperuricemia can result from defect of which enzymes? (Page 339) A. Ribosyl amido transferase, PRPP synthetase, HGPRTase, APRTase, Glucose-6-phosphatase, and glutathione reductase. Q. Hyperuricemia is observed in which conditions? (Page 339) A. Gout, Lesch Nyhan syndrome, von Gierke’s disease. Q. What are salient features of Lesch-Nyhan syndrome? (Page 340) A. Self mutilation, hyperuricemia, and X-linked inheritance. Q. What is the mechanism of action of allopurinol? (Page 340) A. It is an analogue of hypoxanthine. It inhibits xanthine oxidase, and thereby decreasing the formation of uric acid. Q. It is what type of inhibition? (Page 340) A. Xanthine oxidase converts allopurinol to alloxanthine. It is a more effective inhibitor of xanthine oxidase. This is a good example of ‘suicide inhibition. Q. Hypouricemia can result from deficiency of which enzyme? (Page 340) A. Adenosine deaminase deficiency. Q. How is it manifested? A. Severe immunodeficiency.

(Page 340)

214 Viva—based on Textbook of Biochemistry Q. What are used for pyrimidine synthesis? (Page 340) A. Carbamoyl phosphate and aspartic acid. Q. What is the rate limiting step in pyrimidine synthesis? (Page 340) A. Aspartyl trans carbamoylase. Q. What is carbamoyl phosphate synthetase II and how is it different from type I enzyme? (Page 341) A. CPS-II is involved in pyrimidine synthesis, but CPS-I is for urea synthesis. CPS-II is in cytosol, but CPS-I is in mitochondria. CPS-II is inhibited by CTP, whereas CPS-I is not. Q. How is pyrimidine synthesis pathway regulated in mammals? A. CPS II is inhibited by CTP. (Page 341) Q. What is the mechanism of action of 6-mercpto purine? (Page 342) A. It inhibits conversion of IMP to AMP, and so acts as an antimetabolite. Q. What is the mechanism of action of 5-fluoro uracil? (Page 342) A. It inhibits conversion of dUMP to dTTP, and acts as an antimetabolite. Q. Orotic aciduria is a feature of deficiency of which enzymes? (Page 342) A. OMP decarboxylase, OPRTase, and ornithine transcarbamoylase.

Molecular Biology I

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Q. What are the characteristic features of orotic aciduria ? (Page 342) A. Megaloblastic anemia, urinary tract obstruction, and response to oral uridine therapy. Q. Formation of dTMP (thymine nucleotide) requires what enzyme and co-enzymes? (Page 342) A. Methylation of dump is done by thymidylate synthase. The methyl group is donated by methylene-THFA. Later, THFA is regenerated by dihydrofolate reductase, using NADPH. Methotrexate inhibits dihydrofolate reductase and thereby reduces the regeneration of THFA, and it is a powerful anticancer agent. Q. How deoxyribonucleotides are formed? (Page 342) A. By the reduction at the 2' carbon of the corresponding nuceloside diphosphates (NDP to dNDP). Q. What are the enzymes and co-enzymes for this reaction? (Page 342) A. Ribonucleotide reductase, NADPH, and thioredoxin.

216 Viva—based on Textbook of Biochemistry

Molecular Biology-II:

DNA structure and Replication Q. What are the important characteristics of WatsonCrick model of DNA? (Page 344) A. Right-handed double helix, each turn of helix has 10 base pairs, Hydrogen bonds between purines and pyrimidines, and DNA strands running in opposite directions (anti parallel). Q. What is base pairing rule? (Page 344) A. Pairing (hydrogen bonding) of adenine with thymine and guanine with cytosine. Purine is paired with pyrimidine A+T = G+C. Q. What are the modifications seen in histones? (Page 345) A. Acetylation, methylation, and phosphorylation. Q. What is nucleosome? A. DNA wrapped around histones.

(Page 345)

Molecular Biology-III II

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Q. What is euchromatin? (Page 346) A. Transcriptionally active chromatin is called euchromatin. It is less densely packed, and sensitive to digestion by DNAse. Q. What is meant by DNA replication? (Page 346) A. During cell division, each daughter cell gets an exact copy of the genetic information of the mother cell. This process of copying the DNA is known as DNA replication. Q. How the exact copying is effected? (Page 346) A. Each strand serves as a template or mould, over which a new complementary strand is synthesised. The base pairing rule is always maintained. Q. What are the enzymes required for DNA replication? (Page 347) A. DNA polymerase, topo isomerase, and DNA ligase. Q. How many DNA polymerases are there in mammalian cells? A. Five. Alpha, beta, gamma, delta, and epsilon. (Page 347) Q. What a replisome? (Page 347) A. DNA replication needs the participation of more than 20 enzymes and proteins, collectively called DNA replicase system or replisomes. Q. What is a replication bubble? (Page 348) A. Helicases move on both directions, separating the strands in advance of the replication. This forms a replication bubble.

218 Viva—based on Textbook of Biochemistry Q. Replication is in which direction? (Page 347) A. Polymerisation of the new strand of DNA is taking place from 5' to 3' direction. This means that the template is read in the 3' to 5' direction. Q. How replication starts? (Page 347) A. An RNA primer, about 100-200 nucleotides long, is synthesised by the RNA primase. Q. What is meant by semiconservative nature of replication? (Page 346) A. In the daughter cell, one strand is derived from the mother cell, while the other strand is newly synthesised. This is called semi-conservative type of DNA replication. Q. What is meant by semi-discontinuous nature of replication? (Page 348) A. DNA synthesis is always in the 5' to 3' direction in both strands. Replication fork advances towards one side. So, in one strand, the replication is taking place continuously, but in the other strand replication is in small pieces. Q. What is lagging strand? (Page 348) A. The strand which is discontinuously synthesised is referred to as the “lagging strand” and the one continuously polymerised as the “leading strand”. Q. What are okazaki fragments? (Page 348) A. The small DNA molecules attached to its own primer RNA in the lagging strand are called okazaki fragments. The RNA is removed and DNA pieces are joined by ligases.

Molecular Biology-III II

219

Q. Xeroderma pigmentosum is due to deficiency of what process? (Page 349) A. Defect in DNA repair mechanism (nucleotide excision repair). Q. Defect in DNA repair mechanisms produce what clinical conditions? A. Xeroderma pigmentosum, ataxia-telangectasia, Fanconi’s anemia, and Bloom’s syndrome. (Page 350) Q. Which enzymes protects cellular ageing? (Page 350) A. Telomerase. Q. In prokaryotes, DNA replication is inhibited by what drugs? A. Ciprofloxacine, nalidix acid, and novobiocin. (Page 350) Q. DNA replication in eukaryotes is inhibited by what drugs? (Page 350) A. 5-fluoro uracil, 6-mercaptopurine, cytosine arabinoside, and etoposide.

220 Viva—based on Textbook of Biochemistry

Molecular Biology-III:

Transcription and Translation Q. What is transcription? (Page 351) A. The process of making a complementary mRNA copy of DNA. Q. The mRNA is a complementary copy of which strand of DNA? A. Template strand. (Page 351) Q. What is coding strand? (Page 351) A. The opposite strand of template strand. Coding strand has the same sequence as of the mRNA. Q. What is the enzyme necessary for the transcription? (Page 351) A. DNA dependent RNA polymerase or RNAP. Q. What are the different types of RNAP? (Page 351) A. RNAP type II or B is the enzyme synthesising mRNAs. RNAP type I or A is responsible for synthesis of rRNA while type III or C is responsible for production of tRNA.

Molecular Biology-III

221

Q. What is the specific inhibitor of RNAP? (Page 352) A. RNAP II is inhibited by alpha amanitin. Q. What is the direction of transcription?(Page 352) A. It takes place in the 5' to 3' direction. Q. What is TATA Box? (Page 352) A. It is a signal for initiation of transcription in prokaryotes. It is about 10 bp upstream of starting of mRNA synthesis. It is also called pribnow box. Q. What is the corresponding signal in mammals? (Page 352) A. Godberg-Hogness Box. It is located at -25 to -30 position. Q. How termination of transcription is effected? (Page 353) A. The specific signals are recognised by a termination protein, the Rho factor, then the RNAP enzyme dissociates from DNA. There is also Rho Independent Termination. This is effected by an interrupted invert repeat in DNA. This is transcribed. So the mRNA makes a hairpin structure. This obstructs further movement of RNA. Q. What are post-transcriptional modifications? (Page 353) A. Removal of introns, addition of a cap at 5' end, adding poly A tail at 3' end and methylation. Q. What are the non-coding sequences? (Page 354) A. Leader sequence, poly-A tail, introns. Q. What is intron? (Page 354) A. Part of mRNA that is removed is called intron.

222 Viva—based on Textbook of Biochemistry Q. What is a spliceosome? (Page 354) A. Small nuclear ribonucleoprotein particles (SnRNPs) associated with hnRNA at the exonintron junction form spliceosomes. This is taking place inside the nucleus. Q. What is the cause for systemic lupus erythematosis? (Page 354) A. Production of auto antibodies against small nuclear ribonucleoprotein particles cause systemic lupus erythematosis (SLE), a fatal autoimmune disease. Q. What are ribozymes? (Page 354) A. Enzymes made up of RNA are called ribozymes. Q. Give some examples of ribozymes. (Page 354) A. Spliceosomes, RNAse-P (which generates the ends of tRNAs) and peptidyl transferase (present in ribosomes) are examples of ribozymes. Q. Give the names of inhibitors of RNA synthesis. (Page 354) A. Rifampicin, actinomycin, mitomycin and amanitin. Q. What is the mechanism of action of mitomycin? (Page 354) A. Actinomycin D and mitomycin intercalate with DNA strands, thus blocking transcription. They are used as anticancer drugs. Q. What is the mechanism of action of Rifampicin? (Page 354) A. It binds to beta subunit of RNA polymerase, and inactivates it. Rifampicin is widely used in the treatment of tuberculosis and leprosy.

Molecular Biology-III

223

Q. What is the mechanism of action of amanitin? (Page 354) A. It inactivates RNA polymerase II. Q. What is reverse transcriptase? (Page 354) A. In retroviruses, RNA is the genetic material (not DNA). The RNA dependent, DNA polymerase or reverse transcriptase will make a new DNA strand based on the RNA template. Thus, genetic information is transferred from RNA to DNA. Q. Give an example of retrovirus. (Page 355) A. The human immunodeficiency virus (HIV) causing AIDS is a retrovirus. Q. What are the structural features of tRNA molecule? (Page 355) A. It has clover shape appearance. It contains unusual bases. Amino acid binding is at 3' end. The opposite part has anticodon arm. Q. During protein synthesis, amino acid sequence is specified by what? A. The codons present in messenger RNA. (Page 355) Q. During replication, DNA is synthesised in which direction? (Page 356) A. From 5' to 3' direction. Q. During transcription, mRNA is synthesised in which direction? A. From 5' to 3' direction. (Page 356)

224 Viva—based on Textbook of Biochemistry Q. During translation, protein is synthesised in which direction? A. From amino terminal end to carboxy terminal end. (Page 356) Q. What are the salient features of genetic code? (Page 356) A. Triplet codons are consecutive three bases pairs in mRNA. The codons are non-overlapping, degenerate, but unambiguous and universal. Q. What is meant by degeneracy of genetic code? (Page 356) A. One amino acid is represented by multiple codons. Q. What is meant by the term wobbling?(Page 357) A. Anticodons pair with codons that differ at the third base. Q. What is the initiating codon for protein synthesis? (Page 357) A. AUG. Q. What is Shine-Dalgarno sequence? (Page 357) A. Marker of start signal for translation in bacterial mRNA. Q. Where is protein biosynthesis taking place? (Page 358) A. Ribosomal assembly either attached to endoplasmic reticulum, or in cytoplasm. Q. How many high energy bonds are required for the synthesis of one peptide bond? (Page 359) A. Four high energy bonds.

Molecular Biology-III

225

Q. Give examples of diseases caused by protein targetting defects. A. Zellweger syndrome, adrenoleukodystrophy and primary hyperoxaluria. (Page 360) Q. What is the function of signal peptide? (Page 360) A. Causes anchorage of ribosome to endoplasmic reticulum, and so directs the new protein into the endoplasmic reticulum. Such proteins are destined for secretion. Q. What is the location of signal peptide? (Page 360) A. In the amino terminal region of the nascent protein. Q. What is the location of the address for destination of proteins? A. These are in the carboxy terminal end of proteins. (Page 360) Q. Give examples for post-translational modifications. (Page 361) A. Gamma carboxylation of prothrombin, hydroxylation of proline in collagen, methylation of histones, and glycosylation of proteins. Q. Give examples of diseases produced by defect in post-translational modifications. (Page 361) A. Lathyrism, Ehlers-Danlos syndrome, and scurvy. Q. Give examples of inhibitors of translation in eukaryotic cells? A. Puromycin, cycloheximide, diphtheria toxin, and ricin. (Page 361)

226 Viva—based on Textbook of Biochemistry Q. What is the mechanism of action of erythromycin? (Page 361) A. Inhibition of translocation in prokaryotes. Q. What is the mechanism of action of tetracycline? (Page 361) A. Inhibition of tRNA binding to ribosome in bacteria. Q. What is the mechanism of action of streptomycin? (Page 361) A. Misreading of codes and inhibition of initiation complex formation in bacteria. Q. What is the mechanism of action of chloramphenicol? (Page 361) A. Inhibition of peptidyl transferase in bacteria. Q. Give examples of reversible inhibitors of protein synthesis in bacteria. A. These antibiotics are bacteriostatic. Tetracyclins, chloramphenicol, erythromycin and clindamycin are examples. (Page 361) Q. Give an example of irreversible inhibitor of protein synthesis in bacteria. (Page 361) A. These antibiotics are bactericidal. Streptomycin is an example. Q. Leber’s hereditary optic neuropathy is due to what? (Page 362) A. Due to mutation in mitochondrial DNA.

MolecularBiology-IV Biology-V Molecular

227

Molecular Biology-IV: Molecular Genetics and Control of Gene Expression

Q. Give examples of X-chromosome linked transmission. (Page 364) A. Hemophilia, glucose-6-phsophate dehydrogenase deficiency, and duchenne type muscular dystrophy. Q. What is a mutation? (Page 366) A. An alteration in the genetic material results in a mutation. Q. Give an example. (Page 366) A. HbS or sickle-cell hemoglobin is produced by a mutation of the beta chain in which the 6th position is changed to valine, instead of the normal glutamate. Q. What type of mutation is it? (Page 366) A. Here, the normal codon GAG is changed to GUG (transversion).

228 Viva—based on Textbook of Biochemistry Q. Give an example for an unacceptable mutation. (Page 366) A. Haemoglobin M. Q. Give examples for mutagens. (Page 367) A. Acridine orange, X-rays, gamma rays, and methyl cholanthrene. Q. How mutagenecity of a compound is tested? (Page 367) A. By Ame’s test. Q. In which phase of the cell cycle, DNA synthesis is maximum? A. S phase. (Page 368) Q. What is the p53? (Page 368) A. It is an oncosuppressor gene product. Q. Give examples of enzyme induction. (Page 370) A. Beta galactosidase by lactose, tryptophan pyrrolase by glucocorticoid and ALA synthase by barbiturates. Q. Give an example of repression. A. ALA synthase by heme.

(Page 370)

Q. Give names of some important antiviral drugs. (Page 371) A. Acyclovir, Ribavirin, Zidovudine. Q. What is a prion? (Page 372) A. “Prions” is the acronym for “proteinaceous infective particles”.

Molecular Biology-V

229

Molecular Biology-V:

Recombinant DNA Technology and Gene Therapy

Q. What are the uses of recombinant DNA technology? (Page 374) A. Quantitative preparation of bio-molecules, especially human proteins. Risk of contamination is eliminated, when preparing such biomolecules. Specific probes for diagnosis of diseases can be prepared. It is used in gene therapy. Q. What are restriction endonucleases? (Page 374) A. Restriction endonucleases are referred to as “molecular scissors”. These enzymes recognise specific sequence with palindrome arrangement in the double stranded DNA, and then cleave at those sites. They are useful in recombinant DNA technology. Q. What are required for preparing a recombinant DNA molecule? A. Restriction endonuclease, plasmid vector, and DNA ligase. (Page 375)

230 Viva—based on Textbook of Biochemistry Q. How are DNA fragments separated? (Page 378) A. Agarose gel electrophoresis. Q. What is Southern blotting? (Page 378) A. DNA is isolated, fragmented by restriction endonucleases, cut pieces are electrophoresed in agarose gel, then blotted over to a nitrocellulose membrane, when single-stranded DNA will be adsorbed in the nitrocellulose membrane. The radio active probe is placed over the membrane. The membrane is then thoroughly washed and autoradiographed. Q. What is the use of Southern blotting?(Page 378) A. To identify abnormal genes, to demonstrate virus integration, prenatal diagnosis. Q. Give some examples of genetic diseases that could be identified by Southern blotting. (Page 379) A. Sickle cell anemia, Huntington’s chorea, Duchenne muscular dystrophy. Q. What is Northern blotting? (Page 379) A. The Northern blot is used to demonstrate specific RNA. Q. What is Western blotting? (Page 379) A. In this technique, proteins (not nucleic acids) are identified. The proteins are isolated from the tissue and electrophoresis is done. The separated proteins are then transferred on to a nitrocellulose membrane. After fixation, it is probed with radioactive antibody and auto-radiographed.

Molecular Biology-V

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Q. What is meant by the term cloning? (Page 379) A. The term cloning has two broad meanings. When a gene of higher organism is introduced into a bacterial DNA, it is called “cloning of the gene” or “molecular cloning”. When a cell from an animal is grown to an exact duplicate of that animal, it is known as “cloning of an animal” or “somatic cloning”. Q. What are the applications of cloning of animals? (Page 379) A. Animals with genetically desirable traits could be bred more efficiently, e.g. cows yielding more milk. Cows or goats may be genetically engineered to produce milk containing any human protein. Q. RFLP (restriction fragment length polymorphism) is used for what? A. Locating mutations in DNA. (Page 381) Q. What is the application of DNA fingerprinting? (Page 381) A. It has medico-legal application. Q. What are the vectors used for gene therapy? (Page 381) A. Retrovirus, adenovirus, and plasmid liposome complex. Q. Give some diseases in which gene therapy is used successfully? A. Severe combined immuno deficiency, duchenne muscular dystrophy, cystic fibrosis, familial hypercholesterolemia, and hemophilia.(Page 382)

232 Viva—based on Textbook of Biochemistry Q. What is transgenesis? (Page 383) A. It is a form of germ cell gene therapy. A recombinant DNA segment, containing the desired gene from another species, is introduced into the fertilized ova. The embryos are allowed to develop in the uterus of another animal. Q. What is the technique used for gene amplification? (Page 384) A. Polymerase chain reaction. Q. Which enzyme is required for PCR (polymerase chain reaction)? A. Taq polymerase. (Page 384) Q. What is reverse PCR? (Page 384) A. This allows cDNA synthesis from mRNA followed by PCR amplification. In ordinary PCR, DNA is detected, that DNA could be from a living or non-living organism. But in reverse PCR, mRNA is detected, that means, it is derived from a living organism. Q. What is the use of PCR? (Page 384) A. Diagnosis of bacterial and viral diseases, medicolegal cases, diagnosis of genetic disorders, especially prenatal diagnosis. Only very minute quantity of sample is required.

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Biochemistry of AIDS Q. What is the full form of AIDS? (Page 387) A. Acquired immuno deficiency syndrome. Q. What is the causative organism of AIDS? (Page 387) A. Human immunodeficiency virus. Q. How can you detect window period of the disease? (Page 387) A. In the window period viral capsid antigen (p24) can be detected Q. What are the usual laboratory findings in the diagnosis of AIDS? A. The antibodies against gp120 are detected by the ELISA test. To rule out the false positive test, the ELISA positive blood, is then retested with Western blot analysis. (Page 388)

234 Viva—based on Textbook of Biochemistry Q. What other special tests could be done? (Page 388) A. T-helper cell count is below 300/ cu.mm. By RTPCR (reverse transcriptase polymerase chain reaction, the number of HIV particles in blood can be estimated, a value of less than 5000 copies per ml of blood has good prognosis, while a count more than 1 lakh per ml means very bad prognosis. Q. HIV belongs to which group of virus?(Page 388) A. It is a retrovirus. It is an RNA virus. Q. What is the characteristic of retrovirus? (Page 388) A. It contains the enzyme reverse transcriptase. Q. How the virus gets entry into the tissue cells? (Page 388) A. The gp 120 of the virus envelope will specifically bind with CD4 molecules on the surface of target cells. CD4 acts as a receptor for the virus. Q. Where is CD4 molecules present? (Page 388) A. The CD4 molecules are present on the surface of T-helper cells. Q. What are the major groups of anti-HIV drugs available? (Page 390) A. Reverse Transcriptase (RT) inhibitors and protease inhibitors. Q. How RT inhibitors are classified? (Page 390) A. nucleoside analogues, non-nucleoside analogues and nucleotide analogues.

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Biochemistry of Cancer Q. Name some chemical carcinogens. (Page 391) A. Methyl cholanthrene, aflatoxins, benzopyrenes. Q. Name some physical carcinogens. A. X-ray, gamma-ray and UV-ray.

(Page 393)

Q. Name some anti-mutagens and anti-carcinogens. (Page 393) A. Vitamin A, Vitamin C, Vitamin E, and curcumin. Q. Name some oncogenic viruses. (Page 393) A. Epstein Barr virus (EBV), hepatitis B virus(HBV), and human papilloma virus. Q. What are Oncogenes? (Page 394) A. Genes capable of causing cancer. Oncogenes are specific sequences in DNA which when expressed may produce cancer. Q. What are proto-oncogenes? (Page 394) A. Oncogenes present in normal cells are also called as proto-oncogenes.

236 Viva—based on Textbook of Biochemistry Q. Proto-Oncogenes may be activated by what mechanisms? (Page 395) A. Viral infection, mutation in proto-oncogene, promoter insertion, and chromosome translocation. Q. Name a cancer, produced by the deletion of an oncosuppressor gene? A. Retinoblastoma. (Page 396) Q. What are tumour markers? (Page 398) A. They are factors released from the tumour cells, which could be detected in blood and therefore indicate the presence of the tumour in the body. Q. What is the clinical application of tumour markers? (Page 398) A. They are useful for the following purposes. (1) For follow up of cancer and to monitor the effectiveness of the therapy. (2) To detect the recurrence of the tumour Q. Name some important tumour markers. (Page 399) A. Alpha feto protein, carcino embryonic antigen, prostate specific antigen, neuron specific enolase, beta chain of human chorionic gonadotropin, and regan iso-enzyme of alkaline phosphatase. Q. Alpha feto protein (AFP) level in serum is increased in which condition? A. Hepatoma. (Page 399) Q. Carcino embryonic antigen level is increased in which type of cancers? (Page 399) A. Colorectal and gastrointestinal cancers.

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Q. What is the significance of beta chain of human chorionic gonadotropin? (Page 399) A. It is a tumour marker for choriocarcinoma. Q. What is the mechanism of action of mitomycin? (Page 400) A. Intercalation with DNA strands. Q. What is the mechanism of action of Methotrexate? (Page 400) A. It is a folic acid antagonist. Q. What is vincristine and vinblastine? (Page 400) A. They are alkaloids from vinca rosea, they interfere with assembly of cytoskeleton and inhibits stathmokinesis (spindle movement), so they are used as anti-cancer drug. Q. What is the mechanism of action of adriamycin? (Page 400) A. It inhibits topo-isomerase.

238 Viva—based on Textbook of Biochemistry

Applications of Radio-isotopes in Medicine Q. What is an Isotope? A. Isotopes of a given element will have different atomic weights, but will have same atomic number. Q. Radiation hazard is mainly due to which type of radiation? A. Alpha radiation. Q. Iodine-125 emits mainly emits which type of radiation? A. Gamma radiation. Q. What is the isotope used for DNA studies? A. P-32. Q. P-32 is used clinically for what purpose? A. To treat polycythemia vera.

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Q. Which radio-active compound is used to measure glomerular filtration rate (GFR)? A. 131-Iodine labelled hippuran. Q. For RIA (radio immuno assay), the radio-active isotope used is: A. 125-Iodine. Q. What is the use of radio active radium in medicine? A. Intracavity application of radiation, such as carcinoma cervix or body of uterus. Q. What is the common source of radiation in teletherapy? A. 137-Cs (caesium) with a half-life of 30 years. Q. What are radiosensitive tumours? A. Lymphomas, Hodgkin’s disease and neuroblastoma are highly radiosensitive. Q. What are the important toxic effects of radiation? A. Leukopenia, thrombocytopenia, and radiation dermatitis.

240 Viva—based on Textbook of Biochemistry

Body Fluids Q. How lactose is synthesised? (Page 407) A. UDP glucose is epimerased to UDP galactose. Then the galactose unit is transferred from UDPgalactose to glucose. This synthesis of lactose in mammary gland is catalysed by lactose synthase. Q. How lactose synthesis is regulated? (Page 407) A. The lactose synthase has two subunits, a catalytic subunit which is a galactosyl transferase and a modifier subunit that is alpha lactalbumin. The level of the modifier subunit is under the control of prolactin. Q. What is the major difference between human and cow’s milk? A. Human milk has higher carbohydrate content than cow’s milk while protein content is less. (Page 407) Q. How is to humanize cow’s milk? (Page 407) A. To humanise cow’s milk, protein is to be diluted and carbohydrate is to be added. Thus, to one cup of cow’s milk, add half a cup of water and two teaspoons of sugar. This will make it comparable to human milk.

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Q. Milk contains which type of fatty acids? (Page 407) A. The fatty acids are mainly saturated, but 50% of them are medium chain fatty acids (Lauric and Myristic acids). Q. What is the advantage of medium chain fatty acids? (Page 407) A. They are easily digested, absorbed and metabolized. Q. What is the major protein in cow’s milk? (Page 407) A. Eighty percent protein of cow’s milk is casein. Q. What type of protein is casein? A. It is a phospho-protein.

(Page 407)

Q. How the phosphate group is attached to protein? (Page 407) A. The phosphate groups are added to the hydroxyl groups of serine or threonine residues. Q. What is whey? (Page 407) A. If milk is acidified and pH lowered to 4.7, the casein is precipitated (iso-electric precipitation). The supernatant is called whey. Q. What are the proteins present in whey? (Page 407) A. Lactalbumin, lactoglobulin and lysozyme.

242 Viva—based on Textbook of Biochemistry

Hormones-I:

Mechanism of Action of Hormones Q. What are G proteins? (Page 410) A. They are involved in signal transduction. Q. How the G proteins work? (Page 410) A. The receptors are in membrane, and binding of hormone causes activation of G protein. Q. How is G protein activated? (Page 411) A. Binding of hormone on receptor causes attachment of GTP to G protein, and thereby G protein is activated. Q. What is the function of activated G protein? (Page 411) A. Activated G protein activates adenyl cyclase. Q. What is the function of adenyl cyclase? (Page 411) A. Adenyl cyclase will produce cyclic AMP. Q. How adenyl cyclase is destroyed? A. By phospho diesterase.

(Page 411)

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Q. How cyclic AMP further works? (Page 411) A. Cyclic AMP activates protein kinase. Q. What is the function of protein kinase? (Page 411) A. It phosphorylates enzymes or target proteins, so that they are activated. Q. Name some hormones which act through cyclic AMP as the second messenger. (Page 410) A. Glucagon, ACTH, TSH, ADH, FSH, LH. Q. Name some second messengers. (Page 412) A. Cyclic AMP, 1,2-diacyl glycerol, inositol triphosphate, and calcium. Q. Name some hormones which act through cyclic GMP as the second messenger. (Page 410) A. ANF (atrial natriuretic factor). Q. Name some hormones that bind to intracellular receptors. (Page 413) A. Glucocorticoids, mineralocorticoids, estrogens, progesterone, androgens, and thyroxin.

244 Viva—based on Textbook of Biochemistry

Hormones-II:

Pituitary Hormones

Q. What are hypothalamic neuropeptides? (Page 414) A. These neurohormones are antidiuretic hormone (ADH) and oxytocin. Q. Name the important hypothalamic releasing factors. (Page 415) A. TRH (thyrotropin releasing hormone), GnRH (gonadotropin releasing hormone), GHRH (growth hormone releasing hormone), somatostatin (growth hormone inhibitory factor), CRF (corticotropin releasing factor), and PIF (prolactin inhibitor factor). Q. Alpha chain of human chorionic gonadotropin (HCG) is shared with what else? (Page 415) A. TSH, FSH, LH and HCG have the common alpha chain, and beta chains are specific.

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Q. What are the hormones produced by anterior pituitary? (Page 415) A. GH (Growth hormone), ACTH (Adrenocorticotropic hormone), LH (Luteinising hormone), FSH (Follicle stimulating hormone), TSH (Thyroid stimulating hormone), MSH (Melanocyte stimulating hormone), and PRL (Prolactin). Q. What is the major effect of growth hormone? (Page 415) A. GH increases the uptake of amino acids by cells, enhances protein synthesis, and produces positive nitrogen balance. The anti-insulin effect of GH causes lipolysis and hyperglycemia. The overall effect of GH is to stimulate growth of soft tissues, cartilage and bone. It is anabolic. Q. Increased secretion of growth hormone will lead to what condition? A. Excess secretion of GH secretion leads to gigantism in children and acromegaly in adults. (Page 415) Q. What is the result of decreased growth hormone secretion? (Page 415) A. Deficiency of GH secretion in early childhood results in pituitary dwarfism. Q. What is the function of FSH? (Page 416) A. FSH stimulates growth of ovarian follicles in females and spermatogenesis (Sertoli cells) in males. Q. What is the function of LH? (Page 416) A. Testosterone in males (secreted by Leydig interstitial cells) and progesterone in females (secreted by corpus luteum), are increased under the influence of LH.

246 Viva—based on Textbook of Biochemistry

Hormones-III: Steroid Hormones

Q. The 11-hydroxylase is required for the synthesis of which hormone? A. Cortisol. (Page 417) Q. The 17-hydroxylase is required for the synthesis of which hormones? A. Cortisol, testosterone, and estradiol. (Page 417 and 418) Q. Which is the precursor of steroid hormones? A. Cholesterol. (Page 417) Q. What are the hormones produced from progesterone? (Page 417) A. Corticosterone, aldosterone, testosterone, and estrogens. Q. Cortisol has how many carbon atoms?(Page 417) A. 21. Q. Aldosterone has how many carbon atoms? (Page 418) A. 21.

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Q. Testerone has how many carbon atoms? (Page 418) A. 19. Q. Estrogen has how many carbon atoms? (Page 418) A. 18. Q. What is the immediate precursor of estrogens? (Page 418) A. Testosterone. Q. What are the structural features of estradiol? (Page 418) A. Cyclopentanophenanthrene ring, total 18 carbon atoms, aromatic character of A ring, and hydroxyl groups on 3rd and 17 carbon atoms. Q. 21-hydroxylase is required for the synthesis of which hormone? A. Aldosterone. (Page 418) Q. What are the effects of glucocorticoids? (Page 419) A. Increased gluconeogenesis, augmented lipolysis, elevated protein breakdown, and depressed immune function

248 Viva—based on Textbook of Biochemistry

Hormones-IV: Thyroid Hormones

Q. What is the precursor of thyroxin? A. Tyrosine.

(Page 423)

Q. Name some antithyroid agents. (Page 423) A. Thiocyanate, perchlorate, and methimazole. Q. How thyroid hormones are produced?(Page 423) A. Tyrosine residues of thyroglobulin are iodinated. Q. What is the function of thyroid stimulating hormone? (Page 423) A. It increases the uptake of iodine by thyroid gland, enhances the oxidation of iodine to iodide, and favours the hydrolysis of thyroglobulin to produce T4. Q. What is the ratio of T4 and T3 in blood? (Page 424) A. Blood concentration of T4 is 70 times more than of T3.

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Q. What are the functions of thyroid hormones? (Page 424) A. Calorigenic effect or thermogenesis and BMR is increased. Q. How this is produced? (Page 424) A. The thermogenic effect is mediated by uncoupling of oxidative phosphorylation. Thyroxine in large quantities can swell the mitochondria. Basal metabolic rate (BMR) is increased. Q. What are the biochemical features of thyroid hormones? (Page 424) A. Thyroxine increases cellular metabolism. Gluconeogenesis and carbohydrate oxidation are increased. Glucose tolerance test shows rapid absorption. Fatty acid metabolism is increased. Q. Deficiency of thyroxine results in which condition? (Page 426) A. Myxedema. Q. What are the salient features of hypothyroidism? (Page 426) A. Decreased T3 level, increased TSH level, lethargy, hypercholesterolemia, weight gain, and decreased basal metabolic rate. Q. What are the characteristic features of primary hyperthyroidism? A. High TSH and T4 levels, increased rate of metabolism, weight loss, tachycardia, fine tremors, sweating, diarrhea, emotional disturbances, anxiety and sensitivity to heat. (Page 426)

250 Viva—based on Textbook of Biochemistry

Clinical Biochemistry-I Q. Why sodium fluoride is used as a preservative of blood for glucose estimation? (Page 427) A. To prevent glycolysis and to prevent loss of sugar. Q. What are the preservatives used in urine sample? (Page 427) A. Formalin, thymol, chloroform, toluene, concentrated HCl and glacial acetic acid are the commonly used urine preservatives. Q. What is optical density? A. Optical density = minus logT.

(Page 428)

Q. What is Beer-Lambert’s law? (Page 428) A. As per Beer’s law, the intensity of the colour is directly proportional to the concentration of the coloured particles in the solution. The Lambert’s law states that the amount of light absorbed by a coloured solution depends on the length of the column or the depth of the liquid through which light passes.

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Q. What is end point analysis? (Page 428) A. Serum sample and reagents are mixed and incubated for a fixed time, to develop the colour optimally. Then, the OD is ascertained and the concentration of the substances is calculated. This is called end point analysis. Q. What is kinetic method? (Page 429) A. Serum and reagents are incubated, and readings are taken at 2 and 3 minutes exactly, and from the difference in OD between the two values, the concentration is calculated. Here the optimum colour is not developed, but is quicker and hence is often used in autoanalysers. Q. What is accuracy? (Page 430) A. Accuracy is the closeness of a result to the true value. Q. What is meant by the term precision? (Page 430) A. Precision refers to the reproducibility of the result. Precision depends on the technique, the reagents, as well as on the technician. Q. What is meant by specificity? (Page 430) A. Specificity of a reaction denotes that only one substance will answer that particular test. Specificity is determined by the method of the analysis.

252 Viva—based on Textbook of Biochemistry

Clinical Biochemistry-II:

Liver and Gastric Function Tests Q. What is the normal serum bilirubin level? (Page 431) A. 0.2 to 0.8 mg/dl. Q. What is the normal blood level of unconjugated bilirubin? (Page 431) A. 0.2-0.6 mg/dl. Q. What is the normal serum level of conjugated bilirubin? (Page 431) A. Less than 0.2 mg/dl. Q. What is latent jaundice? (Page 431) A. Serum bilirubin between 1 mg/dl and 2 mg/dl. Q. Jaundice appears at what level of bilirubin? (Page 431) A. Jaundice appears if the serum bilirubin goes above 2 mg/dl.

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Q. What is meant by van den Bergh’s direct positive test? (Page 431) A. When bilirubin is conjugated, the purple colour is produced immediately on mixing with the reagent, the response is said to be van den Bergh’s direct positive. Q. What is indirect positive van den Bergh’s test? (Page 431) A. When the bilirubin is unconjugated, the colour is obtained only when alcohol is added, and this response is known as indirect positive. Q. What type of bilirubin is present in hemolytic jaundice? (Page 431) A. In hemolytic jaundice, unconjugated bilirubin is increased in serum. Hence van den Bergh’s test is indirect positive. Q. What happens in obstructive jaundice? (Page 431) A. In obstructive jaundice, conjugated bilirubin in serum is elevated, and van den Bergh’s test is direct positive. Q. What about hepatocellular jaundice? (Page 431) A. In hepatocellular jaundice, a biphasic reaction is observed, because both conjugated and unconjugated bilirubins are increased in serum. Q. What are important liver function tests? (Page 432) A. Serum bilirubin, albumin, alkaline phosphatase, urine bile salts, bile pigments and urobilinogen.

254 Viva—based on Textbook of Biochemistry Q. Increase in serum unconjugated bilirubin occurs in which condition? A. Hemolytic jaundice. (Page 433) Q. What are the features of obstructive jaundice? (Page 433) A. Elevated conjugated bilirubin in plasma, presence of bile salts and bile pigments in urine, increased alkaline phosphatase level in blood, and increased cholesterol in blood. Q. Which tests will be positive in a urine of a patient with obstructive jaundice? (Page 433) A. Gmelin’s test, Hay’s test, and Fouchet’s test. Q. What are the enzymes useful in diagnosis of liver diseases? (Page 433) A. Alanine amino transferase, alkaline phosphatase, and gamma glutamyl transferase. Q. What are the salient laboratory findings in a patient with chronic liver disease? (Page 433) A. Serum albumin is lowered, albumin globulin ratio is reversed, and prothrombin time is prolonged. Q. What is the characteristic laboratory findings in alcoholic cirrhosis? A. Elevation of gamma glutamyl transferase level in serum. (Page 433) Q. What are the important stimulants for gastric acid secretion? A. Gastrin, vagus stimulation, and histamine. (Page 434)

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Q. What is alkaline tide? (Page 434) A. When HCl is produced in stomach, bicarbonate level within the cell increases (formed from H2CO3), it is reabsorbed into blood stream. This would account for the alkaline tide of plasma and urine, immediately after meals. Q. What is the maximal gastric acid output? (Page 435) A. It is the acid output in millimol per hour, after the stimulation. Q. What is the upper limit of maximal gastric acid output? (Page 435) A. 30 mmol/ hour in females and 45 mmol/hour in males. Q. What is basal acid output? (Page 435) A. It is the acid output in millimol per hour, in the absence of all intentional stimulation. Q. What is the upper limit of basic acid output? (Page 435) A. 5 millimol/hour in females and 10 millimol in males. Q. Hypo-acidity is found in which conditions? (Page 435) A. Pernicious anemia, carcinoma of stomach, and atrophic gastritis.

256 Viva—based on Textbook of Biochemistry

Clinical Biochemistry-III:

Kidney Function Tests

Q. How much is glomerular filtration rate? (Page 436) A. 120-125 ml per minute. Q. What is the function of glomerulus? (Page 436) A. An ultrafiltrate of the blood is produced in glomerulus, while the cells and proteins are retained in the blood. Q. What is the normal renal threshold value for glucose? (Page 437) A. Blood level of 180 mg/ dl. Q. What is the normal specific gravity of urine? (Page 438) A. 1.015 to 1.025. Q. What is the minimum and maximum specific gravity of urine? A. 1.003 to 1.032. (Page 438)

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Q. What is the specific gravity of urine in chronic renal failure? A. Fixed to 1.010. (Page 439) Q. Specific gravity of urine increased in which condition? (Page 439) A. Acute glomerulonephritis. Q. Polyuria is seen in which conditions?(Page 439) A. Diabetes mellitus, diabetes insipidus, and chronic renal failure. Q. What are the features of chronic renal failure? (Page 439) A. Urine with fixed specific gravity of 1.010, polyuria, increased blood urea and creatinine. Q. Name abnormal substances seen in urine. (Page 439) A. Protein, blood, sugar, ketone bodies, bile salts, bile pigments, and urobilinogen. Q. Proteinuria is seen in which conditions? (Page 439) A. Acute glomerulo nephritis, nephrotic syndrome, pyelonephritis, and multiple myeloma Q. Which test is commonly employed to detect urinary protein? A. Heat and acetic acid test. (Page 439) Q. What is micro-albuminuria? (Page 439) A. When small quantities of albumin (50-300 mg/ day) is seen in urine.

258 Viva—based on Textbook of Biochemistry Q. How proteinurias are classified? (Page 439) A. Glomerular proteinuria, overflow proteinuria, nephron loss proteinuria, tubular proteinuria, and urogenic proteinuria. Q. What is meant by renal clearance? (Page 441) A. Clearance is defined as the quantity of blood or plasma completely cleared of a substance per unit time and is expressed as milliliter per minute. It is the ml of plasma which contains the amount of that substance excreted by the kidney within a minute. Q. How renal plasma flow is measured? (Page 441) A. Para amino hippurate (Diodrast) clearance. Q. What is the correct method for assessing glomerular filtration rate? A. Inulin clearance. (Page 441) Q. What is its disadvantage? (Page 441) A. Inulin has to be infused intravenously throughout the test period. Q. What is the normal value for PAH clearance ? (Page 442) A. About 700 ml/min. Q. What is the best method for assessing glomerular filtration rate? A. Creatinine clearance test. (Page 442) Q. What is the advantage of creatinine test? (Page 442) A. Creatinine is formed spontaneously (nonenzymatic), so the blood level and excretion rate of creatinine is a constant from day to day.

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Q. What is the normal value of creatinine clearance? (Page 442) A. In males 85-125 ml/min and in females 80-115 ml/ min. Q. What is the significance of creatinine clearance? (Page 442) A. A decreased creatinine clearance is a very sensitive indicator of a reduced glomerular filtration rate. Q. What is the normal creatinine level in blood? (Page 442) A. For adult males, 0.7-1.4 mg/dl, for adult females, 0.6-1.3 mg/dl. Q. What is creatinine coefficient? (Page 442) A. It is the urinary creatinine expressed in mg/kg body weight. Q. What is the significance of creatinine coefficient? (Page 442) A. The value is elevated in muscular dystrophy. Q. What is the normal value of creatinine coefficient? (Page 442) A. Normal range is 20-28 mg/kg for males and 1521 mg/kg for females. Q. Urea clearance is lowered in which condition? (Page 443) A. Chronic liver failure. Q. What is the maximum urea clearance value? (Page 443) A. 75 ml/minute.

260 Viva—based on Textbook of Biochemistry Q. What is the standard urea clearance value? (Page 443) A. 54 ml/minute. Q. When do you call it standard urea clearance? (Page 443) A. When the volume of urine formed is less than 2 ml per minute. Q. What is the normal blood urea level? (Page 443) A. 20-40 mg /dl. Q. What is the clinical significance of increased urea level in blood ? A. Urea level is increased in renal failure.(Page 443) Q. How failure of concentrating capacity of urine is measured ? A. Concentration test (Water deprivation test). (Page 444) Q. How is tubular concentrating capacity measured? (Page 444) A. Urine specific gravity. Q. What are the usual tests to assess tubular function? (Page 444) A. Measurement of specific gravity, concentration test, dilution test, acidification test.

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VIVA—based on Vasudevan’s: Textbook of Biochemistry, 3rd Edition © 2001, Jaypee Brothers Medical Publishers (P) Ltd All rights reserved. No part of this publication should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the editors and the publisher. This book has been published on good faith that the material provided by editors is original. Every effort is made to ensure accuracy of material, but the publisher, printer and editors will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters to be settled under Delhi jurisdiction only.

First Edition: 1995 Second Edition: 1998 Third Edition: 2001 Publishing Director: RK Yadav