Key facts & rules

• Enzymes are biological catalysts — protein molecules that speed up reactions without being used up.
• Active site: specific shape that fits only the substrate (lock-and-key model).
• Denaturation: irreversible change in enzyme shape (caused by high temperature or extreme pH) — the active site changes shape.
• Optimum temperature: for human enzymes ≈ 37°C. Above this, denaturation occurs rapidly.
• Optimum pH: varies by enzyme (e.g. pepsin works best at pH 2, salivary amylase at pH 7).
• Substrate concentration: increasing it increases rate until all active sites are occupied (plateau).
• Inhibitors: competitive (block active site) or non-competitive (change shape of active site).