Introduction to Biomolecules
Biomolecules are organic molecules found in living organisms. The major classes tested in NEET are carbohydrates, proteins, lipids, nucleic acids, and vitamins. This chapter typically gives 2–3 questions in NEET.
Carbohydrates
General formula: Cₙ(H₂O)ₙ. Classified as:
- Monosaccharides: Glucose, Fructose, Galactose (cannot be hydrolysed further)
- Disaccharides: Sucrose (glucose + fructose), Maltose (glucose + glucose), Lactose (glucose + galactose)
- Polysaccharides: Starch, Cellulose, Glycogen
Glucose exists in two cyclic forms: α-glucose and β-glucose (anomers). Reducing sugars (glucose, fructose, maltose, lactose) give positive Fehling's test. Sucrose is a non-reducing sugar.
Proteins
Proteins are polymers of α-amino acids joined by peptide bonds (–CO–NH–). Amino acids have both –NH₂ and –COOH groups.
Structure levels:
- Primary: Sequence of amino acids
- Secondary: α-helix or β-pleated sheet (H-bonds)
- Tertiary: 3D folding (disulfide bonds, H-bonds, ionic, van der Waals)
- Quaternary: Two or more polypeptide chains (e.g., haemoglobin)
Denaturation: Loss of biological activity due to unfolding. Caused by heat, pH change, urea.
Enzymes
Biological catalysts (protein in nature, except ribozymes). Key concepts:
- Active site: specific region where substrate binds
- Lock and Key hypothesis (Fischer) and Induced Fit model (Koshland)
- Enzyme inhibition: competitive (same active site) vs non-competitive (different site)
Nucleic Acids
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polynucleotides.
| Feature | DNA | RNA |
|---|---|---|
| Sugar | Deoxyribose | Ribose |
| Bases | A, T, G, C | A, U, G, C |
| Strands | Double | Single |
| Function | Genetic info | Protein synthesis |
Base pairing: A–T (2 H-bonds), G–C (3 H-bonds) in DNA.
Vitamins
Fat-soluble: A, D, E, K. Water-soluble: B-complex, C. Deficiency diseases: Vitamin A → Night blindness; B₁ → Beri-beri; C → Scurvy; D → Rickets; K → Blood clotting defect.