Overview — 10-Sentence Summary — Summary

CB-02 in 10 Sentences

Living systems are composed of four major biomolecule classes: carbohydrates [( $CH_{2}O$ )n], proteins (polymers of 20 amino acids), lipids (hydrophobic molecules), and nucleic acids (polymers of nucleotides).
Carbohydrates are classified as monosaccharides (glucose, ribose), disaccharides (sucrose, lactose, maltose), and polysaccharides with alpha-glycosidic bonds (storage: starch, glycogen) or beta-glycosidic bonds (structural: cellulose, chitin).
Proteins have four structural levels: primary (peptide bonds), secondary (backbone hydrogen bonds forming alpha-helix or beta-sheet), tertiary (R-group interactions including disulphide bonds), and quaternary (multiple subunits — haemoglobin has 4).
Lipids include triglycerides (energy storage, 3 fatty acids + glycerol), phospholipids (amphipathic, form membrane bilayers), and steroids (4-ring backbone, derived from cholesterol, e.g., testosterone, cortisol).
In DNA, adenine pairs with thymine via 2 hydrogen bonds, and guanine pairs with cytosine via 3 hydrogen bonds, with higher GC content conferring greater thermal stability.
RNA uses ribose (not deoxyribose) and uracil (not thymine); types include mRNA (carries code), tRNA (brings amino acids), and rRNA (ribosome component with ribozyme activity).
Enzymes are biological catalysts that lower activation energy without altering equilibrium, $\Delta G$ , or the final concentrations of reactants and products at equilibrium — they only change the rate.
Six enzyme classes are (OTHLIL): Oxidoreductases (redox), Transferases (group transfer), Hydrolases (hydrolysis), Lyases (non-hydrolytic cleavage), Isomerases (rearrangement), Ligases (bond formation with ATP).
Competitive inhibitors bind the active site (increasing Km, Vmax unchanged, overcome by excess substrate), while non-competitive inhibitors bind allosteric sites (Km unchanged, Vmax decreased, not overcome by substrate).
Apoenzyme (protein, inactive) + cofactor (coenzyme such as N $AD^{+}$ /FAD, prosthetic group such as haem, or metal ion) = holoenzyme (active); ribozymes are catalytic RNA molecules that prove not all enzymes are proteins.