Biochem Practice Final

Practice Questions: Biochemistry and Genetics I, Fall 2006

12/1/06

1) Which of the following pairs of enzymes IS NOT INVOLVED in reversible modifications of histone proteins? A) Kinases, phosphatases B) Acetylases, deacetylases C) Sulfatases, desulfatases D) Methylases, demethylases 2) Which of the following elements of a eukaryotic open reading frame is modified by an endonuclease prior to addition of poly-adenosyl-monophosphates (a poly-A tail)? A) Promoter B) Enhancer C) Exon-Intron junction D) exon E) 3'-Untranslated region (3'-UTR) 3) Dr. M has isolated a new protein and determined that it contains a helix-turnhelix protein structure. Which of the following protein functions is suggested by this structural feature? A) Enzymatic; catalytic B) DNA-binding; transcriptional regulation C) RNA-binding; ribosomal D) Plasma membrane receptor; signal transduction 4) Alu sequences in the human genome are ___________________: A) Present in tandem copies. B) Located within telomere sequences only. C) Identified by similarities with the TATA box. D) A major cause for somatic mutations. E) Prevalent junk DNA sequences at many interspersed chromosomal loci. 5) An 8-month-old girl is brought to the pediatrician with badly sun-burned skin. There are various lesions on sun-exposed skin, some of them pre-malignant. This is most likely a problem with A) post-replication mismatch repair B) nucleotide excision repair C) base excision repair D) AP endonuclease E) repair of DNA double-strand breaks

6) A 16-months-old boy of Middle Eastern ancestry is in hospital with a serious lung infection. He had had similar infections during the past 6 months. The records from past checkups show that the boy had been growing normally until the age of 6 months. After that time his growth slowed, and developmental milestones were delayed. Now he is at the 5th percentile of height and weight. His blood hemoglobin concentration is found to be 4%. The transferrin saturation is 75%. Numerous reticulocytes and some normocytes and normoblasts are found in the blood smear. This is most likely A) sickle cell disease B) β-thlassemia major C) α-thalassemia minor D) α-thalassemia major E) iron deficiency anemia 7) The laboratory takes a karyotype after amniocentesis. The lab report mentions prominent satellites but no further abnormalities. In this context, what is meant by “satellites”? A) Blobs of chromatin attached to the short arms of acrocentric chromosomes, usually harmless B) The telomeric heterochromatin, expansions of which correlate with a long lifespan C) Constrictions in a chromosome that are caused by the expansion of microsatellite sequences, sometimes causes disease D) Unusually prominent bands of heterochromatin on autosomes, usually harmless E) Large duplications on the Y chromosome, causing an increased risk of criminal convictions if male-determining genes are duplicated 8) Patients with Down syndrome are prone to develop health problems as they approach an age of about 50 years. The most important of these old-age problems is A) liver failure B) leukemia C) kidney failure D) Parkinson’s disease E) Alzheimer’s dementia 9) A 7-year-old girl is operated on for “inguinal hernia” (a loop of intestine in the inguinal canal). However, much to his surprise the surgeon detects an immature testis. A karyotype taken after surgery turns out to be 46,XY. The likely cause for these surprising findings is

A) deficiency of Műllerian inhibitory factor (MIF) B) translocation of the sex-determining sry gene from the Y chromosome to the X chromosome C) deficiency of desmolase D) a defective androgen receptor E) deficiency of aromatase 10) During cystic fibrosis screening you identify a woman who has two different CF mutations, one in each of the two copies of the gene. This is a case of A) pleiotropy B) double penetrance C) double heterozygosity D) locus heterogeneity E) compound heterozygosity 11) A diabetic patient complains that his insulin injections don't improve his energy level. The patient's enzymes are assessed for normal activities. Which change in enzyme activity is MOST LIKELY to explain the patient's unresponsiveness to insulin? A) A mutant enolase enzyme which is not responsive to fluoride B) A mutant pyruvate carboxylase enzyme which is not responsive to acetyl-CoA C) A mutant PFK-1 enzyme which is not responsive to changes in pH D) A mutant PFK-2 enzyme which is not responsive to changing cAMP levels E) A mutant Aldolase B enzyme which has three times the normal Km value for fructose 1-phosphate 12) Cyanide leaching of gold ores from mining activity in the Western United States is used to concentrate this rare metal. However, the 'tailings' contain cyanide, posing serious environmental health issues. Cyanide causes toxicity by inhibition of which protein and/or enzyme function? A) The Sodium-Potassium ATPase B) Complex V, ATP synthase (F0 domain) C) The mitochondrial ATP-ADP translocase D) Complex IV, cytochrome oxidase E) The binding of ATP to phosphofructokinase-1 (PFK-1) 13) After a Thanksgiving feast plasma insulin levels increase sharply. Which of the following is an insulin-dependent mechanism of glucose clearance from plasma? A) stimulation of glycogen degradation in liver B) fusion of GLUT4 vesicles with myocyte plasma membranes C) activation of glucuronide biosynthesis in pancreas

D) inhibition of PFK-2 activity in liver E) reduced reuptake of glucose by renal tubules 14) High lactate levels in blood are often associated with reduced oxygen availability to muscle. Which of the metabolic conditions listed below WOULD ALSO result in lactate formation? A) low cellular NADH, and high NAD+ concentration B) high plasma glucagon concentration C) fluorocitrate inhibition of the TCA cycle D) a low ATP/ADP ratio E) low plasma alanine concentration 15) In the following pedigree, which is the MOST LIKELY inheritance pattern of the disease?

A) Autosomal recessive inheritance B) Autosomal dominant inheritance C) X-linked recessive inheritance D) X-linked dominant inheritance 16) No matter which answer you gave to the question above, now assume that the disease is the recessive disease "ataxic cerebral palsy" with a population incidence of 1/10000 (carrier frequency of 2 %). If person II-4 marries an unrelated man, what is her risk of having a baby with ataxic cerebral palsy? A) 1 in 400 B) 1 in 300 C) 1 in 200 D) 1 in 150 E) 1 in 4 17) A representative copy of all mRNA species in a cell type would be found in:

A) A dictionary B) A PCR product produced with primers specific for beta-globin C) A Southern bolt D) A cDNA library E) A genomic library 18) In PCR, which is the correct order of steps in the FIRST cycle? A) Separate DNA strands; make new DNA strand; bind primers B) Make new DNA strand; separate DNA strands; bind primers C) Bind primers; separate DNA strands; make new DNA strand D) Bind primers; make new DNA strand; separate DNA strands E) Separate DNA strands; bind primers; make new DNA strand 19) This family is showing a heritable form of ataxia. What is the MOST LIKELY inheritance pattern of the disease in this family?

I I II A) X-linked-recessive B) Autosomal dominant C) Autosomal recessive D) X-linked dominant E) Y-linked

1

2

3

4

5

20) Changes in globin gene expression occur just after birth, resulting in the production of adult hemoglobin, HbA. This adult form of hemoglobin occurs as a result of: A) Increased α-globin chain synthesis B) Deletion of the β-globin gene cluster C) Replacement of γ-globin synthesis by β-globin synthesis. D) Production of tetramers with an (α β γ ε) subunit composition.

E) Synthesis of globin genes which produce a β2γ2 tetramer with higher oxygen affinity. 21) The partial pressure of carbon monoxide has an important role in oxygen delivery (Bohr effect) because: A) Hemoglobin has a higher p50 value in the presence of higher proton concentration. B) Carbon monoxide binds 'irreversibly' at the oxygen binding site of hemoglobin. C) The partial pressure of CO2 in the pulmonary capillaries is high. D) CO2 binds to the BPG binding site of the hemoglobin tetramer. E) Reduced carbon monoxide in the peripheral tissues results in lower hemoglobin saturation with oxygen. 22) Shown below is the result of an experiment demonstrating the inhibition of alanine transaminase actiivty by a drug. The drug can be identified as a competitive inhibitor of the enzyme activity because in the presence of the drug:

A) The Vmax value is higher B) The Km value is lower C) The Vmax value is lower D) The Km value is higher E) The Km is equal to the substrate concentration at which the velocity is halfmaximal. 23) Which of the following steps in protein synthesis requires GTP? A) Aminoacyl-tRNA synthase activation of amino acids B) Translocation of tRNA-nascent protein complex from the A to the P site C)Attachment of ribosome to endoplasmic reticulum D) Attachment of mRNA to ribosomes E) Attachment of signal recognition particle to ribosomes

24) The Wobble hypothesis allows some tRNAs to recognize more than one codon. Which of the properties of the genetic code supports this hypothesis? A) It is universal B)It is commaless C) It is degenerate D) It is unambiguous E) It is collinear

Answers: C, E, B, E, B, B (6), A, E, D, E, D, D (12), B, C, A, B, D, E (18), B, C, A, D, B, C (24)