CB-02 — NEET Rapid Revision (Most Tested Concepts)

CARBOHYDRATES — HIGH YIELD

• Formula: ($CH_{2}O$)n
• Monosaccharides: Glucose, Fructose, Galactose (hexoses); Ribose (RNA), Deoxyribose (DNA) (pentoses)
• Disaccharides: Sucrose (Glc+Fru), Lactose (Gal+Glc), Maltose (Glc+Glc)
• Polysaccharides: Starch/Glycogen = alpha-linked (storage). Cellulose/Chitin = beta-linked (structural)
• Glycogen = animal starch (liver and muscle). Starch = plant storage (amylose + amylopectin)
• Cellulose → plant cell wall. Chitin → fungi + arthropods
• Sucrose = non-reducing sugar (no free anomeric carbon)

PROTEINS — HIGH YIELD

• 20 amino acids. Joined by peptide bonds (dehydration synthesis)
• n amino acids → (n-1) peptide bonds
• Primary = peptide bonds | Secondary = H-bonds (α-helix/β-sheet) | Tertiary = R-group interactions | Quaternary = multiple chains
• Keratin = alpha-helix. Silk fibroin = beta-sheet. Haemoglobin = quaternary (2α + 2β subunits)
• Disulphide bonds = COVALENT = stabilize tertiary structure = between CYSTEINE residues

NUCLEIC ACIDS — HIGH YIELD

• DNA: Deoxyribose, Thymine, Double-stranded, stable
• RNA: Ribose, Uracil, Single-stranded (usually)
• Chargaff: A=T (2 H-bonds), G=C (3 H-bonds). AT+GC = 100%
• Higher GC content = higher melting temperature = more stable

ENZYMES — HIGHEST YIELD

• MOST TESTED: "Enzymes lower ACTIVATION ENERGY only — NOT $\Delta G$, NOT equilibrium"
• SECOND MOST TESTED: "Ribozyme = RNA enzyme. Not all enzymes are proteins."
• Six classes: OTHLIL (Over The Hill Lies Ice Lake)
• pH optima: Pepsin = pH 2 (stomach). Trypsin = pH 8 (small intestine)
• Competitive inhibition: Km increases, Vmax unchanged, OVERCOME by excess substrate
• Non-competitive inhibition: Km unchanged, Vmax DECREASES, NOT overcome by substrate
• Malonate → competitive inhibitor of succinate dehydrogenase
• Apoenzyme + Cofactor = Holoenzyme
• N$AD^{+}$ = coenzyme (from niacin/B3). FAD = coenzyme (from riboflavin/B2). Haem = prosthetic group
• Induced fit model (Koshland 1958) is NOW MORE ACCEPTED than lock-and-key (Fischer 1894)

LIPIDS — MEDIUM YIELD

• Triglyceride = glycerol + 3 fatty acids (ester bonds) → energy storage
• Phospholipid = glycerol + 2 fatty acids + phosphate group → amphipathic → membrane bilayer
• Steroids = derived from cholesterol (4 ring backbone)
• Saturated FA = no double bonds = solid. Unsaturated FA = C=C bonds = liquid

LAST-MINUTE CRITICAL FACTS

1. Enzyme + equilibrium → NO change in equilibrium (answer to "what doesn't change")
2. Ribozyme → RNA, not protein (answer to "not a protein" MCQ)
3. Competitive inhibitor → overcome by substrate; Non-competitive → cannot be overcome
4. Glycogen = animal (not plant). Chitin = fungi/arthropods (not plant cell walls)
5. AT = 2 H-bonds; GC = 3 H-bonds → more GC = more stable DNA