01Temperature and pH
Rate rises with temperature (more collisions) up to an optimum. Above it, heat breaks hydrogen and ionic bonds holding the shape — the enzyme denatures and activity crashes.
Each enzyme has an optimal pH: pepsin (stomach) ~2, trypsin (small intestine) ~8. Wrong pH changes the charges of R groups and disrupts the active site.
02Concentration and inhibitors
More substrate increases rate until all enzymes are busy (saturation). More enzyme raises the maximum.
Competitive inhibitors look like the substrate and block the active site — overcome by adding more substrate. Noncompetitive inhibitors bind elsewhere (an allosteric site), change the enzyme's shape, and can't be outcompeted.
Cofactors (metal ions like Mg²⁺, Zn²⁺) and coenzymes (organic, often vitamin-derived like NAD⁺) are helpers some enzymes need.
03Notebook box
Competitive: same site, Vmax reachable with lots of substrate. Noncompetitive: different site, Vmax lowered.
Worked example: Adding more substrate restores rate in the presence of inhibitor X but not Y. → X is competitive; Y is noncompetitive.