Biochemistry: Biomolecules, Metabolism and Natural Substances
What you must understand
Know the four main biomolecule classes. Carbohydrates: monosaccharides (glucose, fructose), disaccharides (sucrose, lactose, maltose) with glycosidic bonds, polysaccharides (starch, glycogen, cellulose) and their functions. Lipids: fats/oils as triglycerides (glycerol + fatty acids), saturated vs unsaturated, phospholipids and steroids.
Proteins: amino acids with amino and carboxyl groups, peptide bonds, primary to quaternary structure, denaturation. Enzymes as biological catalysts with active sites, specificity, and factors affecting rate (temperature, pH, substrate concentration). Nucleic acids: DNA and RNA, nucleotides, complementary base pairing (A–T, G–C in DNA; A–U in RNA).
Metabolism: glycolysis, aerobic respiration (Krebs cycle, oxidative phosphorylation), photosynthesis (light reactions, Calvin cycle), and ATP as energy currency. Know catabolism vs anabolism.
Traps
Don't confuse hydrolysis and condensation (opposite directions). Saturated fats have single bonds only, are solid; unsaturated have double bonds, are liquid. Denaturation destroys higher structure but not peptide bonds. Base pairing rules differ between DNA and RNA (uracil replaces thymine).
Rule of thumb
Biomolecules are polymers built by condensation (releasing water) and broken by hydrolysis (adding water).
Worked example
A dipeptide forms from two amino acids by condensation, releasing one H₂O and creating one peptide bond; complete hydrolysis reverses it.