BIOCHEMISTRY

1. Major Compounds in a Cell

• Carbohydrates and their derivatives

• Fats and their derivatives

• Proteins and their derivatives

• Nucleic acids

2. CARBOHYDRATES

General Formula: (CH₂O)ₙ

• (a) Monosaccharides (Simple sugars)

o Carbon atoms: 3–9

o Types:

▪ Aldoses (Terminal -CHO group)

▪ Aldotriose: Glyceraldehyde

▪ Aldotetrose: Erythrose, Threose

▪ Aldopentose: Arabinose, Ribose, Deoxyribose

▪ Aldohexose: Glucose, Galactose, Mannose

▪ Ketoses (>C=O group)

▪ Ketotriose: Dihydroxyacetone (simplest keto sugar)

▪ Ketohexose: Fructose (sweetest sugar)

• (b) Oligosaccharides (2–10 monosaccharide units)

o Disaccharides: Sucrose, Maltose, Lactose, Cellobiose

o Trisaccharide: Raffinose

o Tetrasaccharide: Stachyose

Details:

o Sucrose: α-Glucose + β-Fructose via α-1,2 linkage (Non-reducing)

o Maltose: 2 Glucose units via α-1,4 linkage (Reducing sugar)

o Cellobiose: 2 Glucose units via β-1,4 linkage (Reducing sugar)

o Lactose: β-D-Glucose + β-D-Galactose via β-1,4 linkage

o Stachyose: 1 Glucose + 1 Fructose + 2 Galactose

• (c) Polysaccharides (High molecular weight, in kiloDaltons)

▪ Starch (Plants): Amylose + Amylopectin

▪ Amylose: Unbranched α-1,4 glucose chain (Helical)

▪ Amylopectin: Branched chain (α-1,4 and α-1,6 linkages)

▪ Glycogen (Animals): Similar to starch but more branched

o Structural Polysaccharides:

▪ Cellulose: β-1,4 glucose polymer

▪ Hemicellulose: Made of arabinose, glucose, galactose, xylose, and

▪ Pectin: Polymer of galacturonic acid (Calcium pectate in cell wall)

3. PROTEINS

• Coined by Berzelius, from Greek "Proteios" meaning "of first rank"

• Polymers of amino acids linked by peptide bonds (–CO–NH–)

Protein Structures:

• Primary: Linear amino acid sequence

• Secondary: Alpha-helix & Beta-pleated sheets (H-bonding between nearby amino

• Quaternary: Association of multiple polypeptides

Types of Proteins:

• Structural:

o Collagen – Muscle

o Keratin – Hair, Wool, Nails

o Fibroin – Silk

o Elastin – Insect wings

• Regulatory: Enzymes

• Transport: Myoglobin, Hemoglobin

Classification:

• Simple Proteins: Only amino acids

• Conjugated Proteins: Protein + non-amino acid (prosthetic group)

o Examples:

▪ Nucleoprotein: Nucleic acid + protein

▪ Glycoprotein: Protein + sugar

▪ Metalloprotein: Protein + metal (e.g., hemoglobin)

4. ENZYMES

• First enzymatic activity discovered by Buchner (zymase)

• Term "enzyme" coined by W. Kuhne

Terminology:

• Holoenzyme = Apoenzyme + Prosthetic group

• Apoenzyme = Inactive enzyme (without prosthetic group)

• Ligand = Substance binding to enzyme

• Active Site = Catalytic site

• Regulatory Site = Controls enzyme activity

Enzyme Characteristics:

• Highly specific, proteinaceous, colloidal

• Sensitive to temperature, pH, ionic strength, water content

• Do not alter equilibrium – only speed it up

Mechanism:

• Lock & Key Model – Proposed by Fischer

Special Enzyme Types:

• Allosteric Enzymes: Regulatory, multimeric, show sigmoidal curve

• Isozymes: Different enzymes for same reaction (tissue-specific, genetically different)

• Ribozymes: RNA with catalytic function (non-protein)

5. VITAMINS

• Term coined by Funk

Classification:

• Water Soluble: B-complex (B₁, B₂, B₆, B₁₂), Vitamin C

• Fat Soluble: Vitamins A, D, E, K

Deficiency Symptoms:

Vitamin Deficiency Symptoms

A (Retinol) Xerophthalmia, Night blindness, Dry

B₁ (Thiamine) Beriberi Weakness, joint pain

B₁₂ Pernicious anemia ↓ RBC

B₆ / Niacin Pellagra Black tongue

C (Ascorbic acid) Scurvy Bleeding gums, weakness

D (Calciferol) Rickets (children), Osteomalacia

E (Alpha-tocopherol) Sterility

Most vitamins function as cofactors in enzymatic activity.

6. NUCLEIC ACIDS

Types:

• DNA: Deoxyribonucleic acid

• RNA: Ribonucleic acid

Components:

• Nucleoside = Sugar (Ribose/Deoxyribose) + Nitrogen base

• Nucleotide = Nucleoside + Phosphate group

Nitrogenous Bases:

• Purines: Adenine (A), Guanine (G)

• Pyrimidines: Cytosine (C), Thymine (T – DNA), Uracil (U – RNA)

Structure:

• Watson & Crick: B-form DNA (right-handed helix)

• Frederick Miescher: First discovered nucleic acids

• Bacteriophage: Can have single-stranded DNA

Types of RNA:

• mRNA: Carries genetic message (5%)

• tRNA: Transfers amino acids to ribosomes

• rRNA: Structural and functional component of ribosomes