Key Points — Carbohydrates and Proteins — Summary

Carbohydrates:

Formula: ( $CH_{2}O$ )n. Ratio C:H:O = 1:2:1
Monosaccharides: Glucose ( $C_{6}H_{12}O_{6}$ ), Fructose (hexoses); Ribose, Deoxyribose (pentoses)
Three key disaccharides: Sucrose (Glu + Fru), Lactose (Gal + Glu, in milk), Maltose (Glu + Glu)
Sucrose is NON-reducing (glycosidic bond locks both reducing groups)
Polysaccharides: Alpha-glycosidic bonds → storage (starch, glycogen); Beta-glycosidic bonds → structural (cellulose, chitin)
Starch = plant storage (amylose: linear; amylopectin: branched). Glycogen = animal storage (most branched)
Cellulose = plant cell wall. Chitin = fungal cell wall + arthropod exoskeleton
Humans: have amylase (cleaves alpha-bonds) but NOT cellulase → cannot digest cellulose
Glycogen branching: every 8-12 glucose units → faster glucose release than amylopectin (every 24-30)
Lactose → hydrolysed by LACTASE. Deficiency causes lactose intolerance

Proteins:

20 amino acids; each has: alpha-C, – $NH_{2}$ (amino), –COOH (carboxyl), –H, –R (variable side chain)
Peptide bond: dehydration synthesis between –COOH of one AA and – $NH_{2}$ of next. Releases $H_{2}O$
n amino acids → (n-1) peptide bonds → (n-1) $H_{2}O$ released
Primary: amino acid sequence (peptide bonds = covalent backbone)
Secondary: alpha-helix or beta-sheet (backbone HYDROGEN BONDS, not R-group interactions)
Tertiary: 3D folding (disulphide bonds, hydrophobic interactions, ionic bonds, H-bonds — all R-group interactions)
Quaternary: multiple polypeptide subunits (haemoglobin: 4 subunits — 2α + 2β chains)
Haemoglobin: each subunit has ONE haem prosthetic group (contains $Fe^{2+}$ ) — quaternary structure
Keratin (hair, nails) → alpha-helix secondary structure. Silk fibroin → beta-pleated sheet
Denaturation: irreversible disruption of secondary/tertiary by heat/pH. Does NOT break peptide bonds
Primary structure determines all higher structural levels (Anfinsen's principle)