Unit 1 covers the chemistry underlying biology — the unique properties of water, the four macromolecules (carbohydrates, lipids, proteins, nucleic acids), and enzymes as biological catalysts.
Water: polar, hydrogen bonding → high specific heat, cohesion, adhesion, universal solvent, ice floats. Monomers join by dehydration synthesis (condensation), break by hydrolysis. Carbohydrates: monosaccharides (glucose), polysaccharides (starch, glycogen, cellulose). Lipids: triglycerides (energy storage), phospholipids (cell membranes), steroids. Proteins: amino acids linked by peptide bonds, 4 levels of structure. Nucleic acids: DNA and RNA, nucleotide monomers.
Biological catalysts: lower activation energy. Substrate binds to active site (induced fit model). Factors: temperature (optimum, denaturation), pH, substrate concentration, enzyme concentration. Competitive inhibition: molecule blocks active site. Non-competitive (allosteric): binds elsewhere, changes active site shape. Cofactors/coenzymes assist enzyme function. Feedback inhibition: product inhibits enzyme earlier in pathway.
Water\'s polar nature and hydrogen bonding give it unique properties essential for life: (1) High specific heat: stabilises temperatures in organisms and environments. (2) Cohesion/adhesion: enables capillary action and transpiration in plants. (3) Universal solvent: dissolves ionic and polar substances for biochemical reactions. (4) Ice is less dense than liquid water: frozen surfaces insulate bodies of water. (5) High heat of vaporisation: evaporative cooling (sweating). These properties make water the medium in which all biochemistry occurs.
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