<h2>Introduction to Biomolecules</h2> <p>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.</p> <h2>Carbohydrates</h2> <p>General formula: Cₙ(H₂O)ₙ. Classified as:</p> <ul> <li><strong>Monosaccharides:</strong> Glucose, Fructose, Galactose (cannot be hydrolysed further)</li> <li><strong>Disaccharides:</strong> Sucrose (glucose + fructose), Maltose (glucose + glucose), Lactose (glucose + galactose)</li> <li><strong>Polysaccharides:</strong> Starch, Cellulose, Glycogen</li> </ul> <p>Glucose exists in two cyclic forms: α-glucose and β-glucose (anomers). <strong>Reducing sugars</strong> (glucose, fructose, maltose, lactose) give positive Fehling's test. Sucrose is a non-reducing sugar.</p> <h2>Proteins</h2> <p>Proteins are polymers of α-amino acids joined by peptide bonds (–CO–NH–). Amino acids have both –NH₂ and –COOH groups.</p> <p>Structure levels:</p> <ol> <li><strong>Primary:</strong> Sequence of amino acids</li> <li><strong>Secondary:</strong> α-helix or β-pleated sheet (H-bonds)</li> <li><strong>Tertiary:</strong> 3D folding (disulfide bonds, H-bonds, ionic, van der Waals)</li> <li><strong>Quaternary:</strong> Two or more polypeptide chains (e.g., haemoglobin)</li> </ol> <p><strong>Denaturation:</strong> Loss of biological activity due to unfolding. Caused by heat, pH change, urea.</p> <h2>Enzymes</h2> <p>Biological catalysts (protein in nature, except ribozymes). Key concepts:</p> <ul> <li>Active site: specific region where substrate binds</li> <li>Lock and Key hypothesis (Fischer) and Induced Fit model (Koshland)</li> <li>Enzyme inhibition: competitive (same active site) vs non-competitive (different site)</li> </ul> <h2>Nucleic Acids</h2> <p>DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are polynucleotides.</p> <table> <tr><th>Feature</th><th>DNA</th><th>RNA</th></tr> <tr><td>Sugar</td><td>Deoxyribose</td><td>Ribose</td></tr> <tr><td>Bases</td><td>A, T, G, C</td><td>A, U, G, C</td></tr> <tr><td>Strands</td><td>Double</td><td>Single</td></tr> <tr><td>Function</td><td>Genetic info</td><td>Protein synthesis</td></tr> </table> <p><strong>Base pairing:</strong> A–T (2 H-bonds), G–C (3 H-bonds) in DNA.</p> <h2>Vitamins</h2> <p>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.</p>