Biomolecules Revision Notes (NEET)

Carbohydrates

• Classification: Monosaccharides (glucose, fructose), Disaccharides (sucrose, maltose, lactose), Polysaccharides (starch, glycogen, cellulose).
• Glucose: aldohexose, D-form, 6C, cyclic pyranose (α/β), open aldehyde reduces Fehling/Tollen.
• Fructose: ketohexose, forms furanose; reduces Tollens (isomerises).
• Sucrose (α-glucose + β-fructose, α,β-1,2 glycosidic) → non-reducing.
• Maltose (α-1,4), Lactose (β-1,4 galactose-glucose) → reducing.
• Starch = amylose (linear α-1,4) + amylopectin (branched α-1,6 branches).
• Cellulose (β-1,4 glucose, humans can't digest).
• Chirality: D/L based on last chiral centre.

Proteins

• Amino acids: 20 essential + non-essential; α-amino, α-COOH; zwitterion at isoelectric pH.
• Peptide bond: −CONH− (planar, partial double bond).
• Structure: 1° (sequence), 2° (α-helix, β-sheet, H-bond), 3° (folded 3D via disulfide, ionic, hydrophobic), 4° (subunits, e.g., Hb).
• Denaturation: loss of 2°/3°/4° (heat, pH, urea).

Enzymes

• Biological catalysts, protein/ribozyme.
• Michaelis-Menten $v = V_{max}[S]/(K_m + [S])$; $K_m$ = substrate at half Vmax.
• Competitive (↑Km, Vmax same), non-competitive (Km same, ↓Vmax).

Nucleic Acids

• Nucleoside = sugar + base; Nucleotide = nucleoside + phosphate.
• Bases: Purines (A, G), Pyrimidines (C, T, U).
• DNA: deoxyribose, T; RNA: ribose, U.
• Chargaff: A=T, G=C.

Vitamins

• Fat-soluble (A, D, E, K); water-soluble (B complex, C).
• Deficiencies: A → night blindness, D → rickets, K → clotting, B1 → beri-beri, B3 → pellagra, B12 → pernicious anaemia, C → scurvy.

Lipids

• Triglycerides, phospholipids, steroids.
• Saturated (solid, animal) vs unsaturated (liquid, plant, contains C=C).

Practice MCQs

Q1. Sucrose is a non-reducing sugar because A) It is a polysaccharide B) Both anomeric carbons are involved in glycosidic bond C) It has no OH group D) It is D-form

Q2. Amylopectin has which type of glycosidic bond at branches? A) α-1,4 B) α-1,6 C) β-1,4 D) β-1,6

Q3. Peptide bond is A) Single bond B) Planar with partial double character C) Fully double bond D) Triple bond

Q4. Enzyme activity is measured by A) Km alone B) Vmax C) Vmax and Km D) Denaturation temp

Q5. Which vitamin deficiency causes rickets? A) A B) B12 C) D D) K

Q6. Number of chiral centres in glucose (open chain) is A) 3 B) 4 C) 5 D) 6

Q7. Ribose differs from deoxyribose by A) Extra CH₃ B) Extra OH at C-2 C) Missing OH at C-1 D) Different chirality

Q8. Denaturation of protein loses A) Primary B) Secondary+tertiary C) Peptide bonds D) All

Q9. Which is an essential amino acid? A) Glycine B) Alanine C) Lysine D) Serine

Q10. Fehling's solution is reduced by A) Sucrose B) Maltose C) Cellulose D) Trehalose

Answers: 1-B (α,β-1,2 glycosidic bond uses both anomeric carbons.), 2-B (α-1,6 at branch points.), 3-B (Resonance makes it planar.), 4-C (Both parameters.), 5-C (Ca-P absorption impaired.), 6-B (C2, C3, C4, C5 → 4 chiral centres.), 7-B (2′-OH present in ribose.), 8-B (Peptide backbone (1°) intact.), 9-C (Lysine cannot be synthesised in humans.), 10-B (Maltose has free anomeric OH.)

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