Enzyme Activity
Enzymes are catalysts, not reactants — they speed up a reaction without being used up. Work through the tabs below at your own pace: the core simulator, the energy diagram behind it, real enzymes your body depends on, how enzymes are classified and what they need to function, and — if you want to go past what the AP exam actually requires — the differential equations enzyme kinetics really follow.
New to protein folding? The Protein Structure lesson covers primary through quaternary structure first — worth reading before this one, since denaturation below is really a story about those levels breaking down.
An enzyme is a biological catalyst — almost always a protein — that speeds up a chemical reaction by lowering its activation energy, the energy barrier a reaction has to clear before it can proceed. Like every protein, an enzyme is built from a chain of amino acids that folds into a precise three-dimensional shape, and its function depends entirely on that shape being correct. It works by binding its substrate (the molecule being acted on) at a pocket called the active site, holding it in a position that makes the reaction easier. Critically, the enzyme itself comes out of the reaction unchanged: it releases its product and is immediately free to bind another substrate molecule. In the simulator above, this is exactly why enzyme particles never disappear — a successful reaction only puts that enzyme on a brief cooldown (its turnover time) rather than consuming it.