UNIT II CHAPTER 2: BIOMOLECULES: BUILDING BLOCKS

All cardinal features of life (movement, sensory perception, digestion etc) are summation of biochemical reactions.

BUILDING BLOCKS OF CARBOHYDRATES: SUGARS AND THEIR DERIVATIVES Glucose, sucrose, fructose Molecular formula are multiples of (CH2O) - carbon hydrates• Molecules having upto six carbon atoms- Monosaccharides.

• MONOSACCHARIDES• Classification based on number of carbon atoms:

1. Trioses- 3 carbon

2. Tetroses- 4 carbon

3. Pentoses- 5 carbon

4. Hexoses- 6 carbon• Classification based on functional group:

1. Aldoses- aldehydic

2. Ketoses-ketonic• Combinations

1. Aldopentose- 5 carbon,aldehydic group

2. Ketohexose- 6 carbon, ketonic group, e.g, fructose

3. Glucose is aldohexose

Configuration• D configuration

• Hemiacetals• Monosaccharides-Hydroxyl and carbonyl group

• React to form hemiacetals.

• Internal hemiacetals- ring structure in pentoses and hexoses

• Furanose-5 membered ring

• Pyranose-6 membered ring

• Fisher projections- Linear projections

• Haworth projections- Ring structures

• Anomeric carbon-Carbon carrying the aldehydic/ketonic oxygen - C1 in glucose, C2 in fructose

• Called anomeric because on formation of ring structure , the carbon atom becomes asymmetric-leads to formation of alpha and beta forms

GLYCOSIDIC BOND

• -OH group of one monosaccharide with -OH group of another-Disaccharide

• Dehydration-elimination of water

• Trisaccharide- 3 sugar residues

• oligosaccharide- 3 - 20 residues

• Polysaccharides- more than 50 residues

PROPERTIES OF SUGARSREDUCING SUGARS

•Sugars with free anomeric carbon

•Reduce alkaline solutions of copper salts to give yellow to red ppt of cuprous oxide - Fehling and Benedict test- pathological labs for sugar in urine /blood

•Sucrose is non reducing

BUILDING BLOCKS OF PROTEINS- AMINO ACIDS

•20 amino acids

•Two functional groups- amino and carboxylic

•Amino group attached to alpha carbon

•Imino group in proline.

•R group is variable

Classification of amino acids

1.Charged- Lysine, arginine, aspartic acid, glutamic acid

2.Polar(with uncharged polar R group)- Serine, asparagine, glutamine

3.Hydrophobic(hydrophobic R group)- Glycine, isoleucine,proline,phenylalanine.

CONFIGURATION

L configuration

PROPERTIES OF AMINO ACIDS• Variety of chemically reactive groups- alpha amino, carboxylic groups, phenolic groups, sulfyhydryl groups .

• Ninhydrin test- reaction between alpha amino group of free amino acid and ninhydrin

oxidative deamination

Ninhydrin (Oxidising agent)+ amino acids ammonia + carbon dioxide + aldehyde + reduced ninhydrin

ammonia + reduced ninhydrin Ruhemann’s purple

• Proline gives yellow colour because has imino group instead of amino group.

IMPORTANT DERIVATIVES OF AMINO ACIDS

1) Neurotransmitters- GABA- gamma amino butyric acid- from glutamic acid

2) Serotonin- hydroxytryptamine from tryptophan

3) Hormones- Thyroxine and adrenaline from tyrosine

4) Plant growth factors- auxins- indole acetic acid from tryptophan

5) Mediators of allergic reactions- Histamine from histidine

VITAMINS AND COENZYMES• Coenzymes

BUILDING BLOCKS OF LIPIDS- SIMPLE FATTY ACIDS, SPHINGOSINE, GLYCEROL AND CHOLESTEROL

1) Constituents of biological membranes

2) Sparingly soluble in water

3) Soluble in organic solvents like chloroform

4) Some building blocks of larger lipids are long chain hydrocarbons containing fatty acids1) stearic acid and oleic acid2) C18 amino alcohols – sphingosine3) Glycerol and cholesterol4) Steroids- derived from cholesterol5) Steroid hormone- estrogens and androgens(testosterone)6) Growth factors and immunosuppressive factors- cortisol

Properties of lipidsUNSATURATED FATTY ACIDS Have double or triple bonds Add halogens across their bonds- decolourize coloured bromine water

Phospholipids are important constituents of membranes- barriers, receptors for cell-cell communication

BUILDING BLOCKS OF NUCLEIC ACIDS: NUCLEOTIDES

1) Nucleotide made of three components:-1) Pentose residue – deoxyribose in DNA and ribose in RNA2) Organic phosphate residue3) Nitrogenous base- Purine or Pyrimidine

Residue- elimination of water during bond formation.

Nitrogenous bases1) Purines and pyrimidines

2) Heterocyclic aromatic ring structure ( Carbon and other elements in the ring)

3) Purine- 1) Adenine and Guanine2) Bonded to sugar phosphate residue by a glycosidic bond involving C-1 of sugar and N-9 of purine and N-1 of

pyrimidine

Properties of nucleotides

1) Orcinol method- Estimation of pentoses:- strong acid Ferric chloridePentose (ribose) + Orcinol Furfural Green coloured compound

2) Diphenylamine method acidic conditionsDeoxyribonucleotides + diphenylamine--------------------------- Blue coloured complex

BIOCHEMICAL TRANSFORMATIONS

S.No Biological reactions Chemical reactions

1 Occur at mild temperatures Occur at high temperatures

2 Occur at atmospheric pressure Occur at high pressures

3 Enzyme catalyzed Catalysts used

4 E.g= oxidoreduction, group transfers, hydrolysis etc

E.g= salt analysis etc

CARBOHYDRATE METABOLISM Plants are auxotrophs Animals are heterotrophs Adenosine triphosphate (ATP) – energy currency of the cell Phosphoanhydride bond between alpha and gamma phosphate groups are hydrolysed

CATABOLISM OF GLUCOSE AND OTHER HEXOSES

Glycolysis