Cellular Chemical Compounds

CHAPTER 4 CELLULAR CHEMICAL COMPOUNDS

Cellular chemical compounds • Four main classes of large biological molecules: carbohydrates, lipids, proteins and nucleic acids also called macromolecules • They are chain-like molecules called polymers : a long molecules consisting of many similar or identical building blocks linked by covalent bonds. • The repeating units that serve as the building blocks of a polymer are small molecules called monomers.

Carbohydrates •

The most important source of energy in a cell

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General formula : CnH2n On

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Consists of carbon, hydrogen and oxygen – 1:2:1

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Include both sugars and polymers of sugars

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Simplest carbohydrates : monosaccharides

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Double sugars : disaccharides – consisting of two monosaccharides joined by a condensation reaction

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Macromolecules : oligosaccharides – consisting two to ten units of monosaccharides polysaccharides - consisting more than ten units of monosaccharides

Monosaccharides •

Few groups: trioses (C3H6O3), pentose (C5H10 O5) and hexoses (C6H12 O6) Example : Hexose - Glucose (C6H12 O6) Act as reducing agents in Benedict and Fehling Tests.

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2 groups : aldose and ketose – depending on the location of the carbonyl group Example : Glucose is an aldose and fructose is a structural isomer of glucose is a ketose

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Characteristics : sweet, water-soluble and can crystallize

Oligosaccharides •

Consists of two or more units of monosaccharides

Disaccharide (important oligosaccharides) •

Consists of two monosaccharides joined by a glycosidic linkage – a covalent bond formed between two molecules by a condensation reaction

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Example: Glucose + glucose → Maltose (Malt sugar in brewing beer) Glucose + fructose → Sucrose (Table sugar) Glucose + galactose → Lactose (sugar in milk)

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Characteristics : sweet, water-soluble and can crystallize

+ H2O

Condensation reaction to form disaccharide - sucrose

Polysaccharides • Macromolecules, polymers with a few hundred to a few thousand monosaccharides joined by glycosidic linkages through condensation reaction • General formula : (C6H12 O6)n • Serve as storage material, hydrolyzed to provide sugar for cells and building material • Characteristics : not sweet, insoluble in water and cannot crystallize

Starch Storage in plants. Consists entirely of glucose monomers. Plants store starch as granules within cellular structures called plastids which include chloroplasts.

Glycogen Similar to amylopectin but more extensively branched. Storage polysaccharide in human and other vertebrates mainly in liver and muscle cells.

Protein •

Consists of C, H, O and N and occasionally S • made up of thousands of polypeptides chains • Basic unit for polypeptide is amino acid connected by peptide bonds Amino acid monomers side chain R α carbon H

O N C C

H amino

OH H group

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carboxyl group

the physical and chemical properties of the side chain determine the unique characteristics of a particular amino

Functions of protein: a.

Building new tissues and replacing dead, injured or damaged tissues

b.

Producing enzymes, antibodies, hemoglobin, carotene and hormones

c.

Produce energy by breaking down protein to carbohydrates

d.

Forming muscles

Sources of protein: Meat, eggs, milk, fish and beans

Formation of Amino acid polymers

H

OH

Condensation

H

OH

Level of Protein Structure The Primary Structure of Protein •

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Example : Transthyretin – a globular protein found in the blood that transport vitamin A and a particular thyroid hormone throughout the body Four identical polypeptide chains make it composed of 127 amino acids

The Secondary Structure of Protein • • •

Composed of coils and folds of polypeptide protein Hydrogen bonds linked the repeating constituents of the polypeptide backbone. Two types: α helix – human hair β pleated sheet – spider silk

The Tertiary Structure of Protein •

Holds by a few type of bonds: Hydrophobic interaction Van der Waals interaction Ionic bond Disulfide bridge

Example: Cytokines, Interleukins, Human growth hormones

The Quaternary Structure of Proteins • •

Include overall protein structure that results from the aggregation of these polypeptide subunits Example : Hemoglobin : consists of four polypeptide subunits, two of one kind (α chains) and two of another kind (β chains)

Review: the four levels of protein structure

Lipid •

Consists of C, H and O and sometimes P

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Types of lipid : fats, phospholipids and steroids

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Characteristics : insoluble in water but soluble in organic solvent; at room temperature, lipid exists in two forms: liquid (oil) and solid (fat)

Fats •

Form from smaller molecules by dehydration reactions

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Constructed from glycerol and fatty acids Fat molecule = three fatty acids join to a glycerol (ester linkage)

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Fat is also called triacylglycerol : three fatty acids + one glycerol

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Fatty acids vary in length and in the number and locations of double bonds

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2 types : saturated and unsaturated fats

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Saturated fatty acid : No double bonds between carbon atoms composing the chain, it is saturated with hydrogen

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Unsaturated fatty acid : has one or more double bonds, form by the removal of hydrogen atoms from the carbon skeleton

Saturated fat •

Mostly animal fats

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Solid at room temperature

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Example : butter

Unsaturated fat •

Mostly from plants and fishes

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Liquid at room temperature

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Example : Olive oil, cod liver oil

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The kinks where the cis double bond are located prevent the molecule from packing closely enough to solidify at room temperature

Function of fats: a. Release twice the energy for each gram of burned fat, compared to carbohydrates. b. Act as heat insulators, for example adipose tissue under the skin c. Provide protection against injuries or concussion to internal organs for example fats around kidney d. Act as the soluble site for fat-soluble vitamins like vitamins A, D, E and K.

Power from animal fat, soybeans, or other forms of biodiesel fuel Designed by Craig Loomes Design Group Ltd

Phospholipids •

Similar to fat but only has two fatty acids attached to glycerol

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The third hydroxyl group of glycerol is joined to a phosphate group which has a negative electrical charge

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Additional small molecules usually charged or polar can be linked to the phosphate group to form a variety of phospholipids

Nucleic Acid •

Two types of nucleic acids : deoxyribonucleic acid (DNA) and ribonucleic acid (RNA)

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These molecules enable living organisms to reproduce their complex components from one generation to the next

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DNA provides directions for its own replication, directs RNA synthesis and control protein synthesis

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DNA is the genetic material that organisms inherit from their parents

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Each chromosome contains one long DNA molecule

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DNA encoded the information that program all the cells activities

The human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes (23 pairs of chromosomes including a pair of sex chromosome) DNA was first isolated by the Swiss physician Friedrich Miescher in 1869 In 1953, James Watson and Francis Crick suggested the first accurate model of DNA structure

The Structure of Nucleic Acids •

Nucleic acids are macromolecules that exists as polymers called polynucleotides

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Each polynucleotides consists of monomers called nucleotides

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Nucleotides composed of three parts : a nitrogenous base pentose (five-carbon sugar) a phosphate group

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Nucleotides are joined by covalent bonds called phosphodiester linkage

a

Nucleotide monomers

Phosphodiester linkage

Nucleotide Polymers •

Nucleotides are joined by covalent bonds called phosphodiester linkage between the OH group on the 3’ carbon of one nucleotide and the phosphate on the 5’ carbon of the next

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The two free ends of the polymers : phosphate attached to a 5’ carbon (5’ end) and a hydroxyl group on a 3’ carbon (3’ end) Phosphodiester linkage

5’C 5’C 3’C

3’C

Base pairing: In DNA Adenine(A) – Thymine(T)

Guanine(G) – Cytosine(C) In RNA Adenine(A) – Uracil (U)

Guanine(G) – Cytosine(C)

Differences between DNA and RNA Characteristics

DNA

RNA

1. Pentose group (sugar)

Deoxyribonucleic acid

Ribonucleic acid

2. Nitrogenous base

Adenine, Thymine, Adenine, Urasil, Guanine and Guanine and Cytosine Cytosine

3. Structure

Longer chain, double stranded

Shorter chain, can be either double (only virus) or single strand

•Urasil replace Thymine in RNA; but the other nitrogen bases no change •

Functions of DNA/RNA • DNA: – Containing genetic information = genes – Synthesis of RNA as well – Genes have coding that help in protein synthesis by RNA – Can be inherited from parents to offsprings; genetic relationship • RNA: • Responsible for protein synthesis

RNA Messenger RNA

Transfer RNA

Ribosomal RNA

Carries information specifying amino acid sequences of proteins from DNA to ribosomes

The RNA that moves amino acids to the ribosome to be placed in the order prescribed by the messenger RNA

RNA that constructed the ribosomal subunit;

3’

Messenger RNA (mRNA)

Helping in protein synthesis

3’

Transfer RNA (tRNA)

Ribosomal RNA (rRNA)