Biology
Enzymes — quick study summary
AP BiologyGCSE BiologyIB Biology HL
Enzymes are biological catalysts (usually proteins) that lower activation energy and speed up chemical reactions without being consumed. Each enzyme has an active site shaped to fit a specific substrate. Activity depends on temperature, pH, substrate concentration and the presence of inhibitors or cofactors.
Key points
- Lower activation energy without changing reaction equilibrium
- Specificity comes from active-site shape (lock-and-key + induced fit)
- Each enzyme has an optimum temperature and pH
- Competitive inhibitors bind the active site; non-competitive bind elsewhere
- Denaturation = permanent loss of active-site shape (high temp / extreme pH)
Practice quiz
Click each question to reveal the answer.
1. What does an enzyme lower to speed up a reaction?
Answer: Activation energy
2. Where does the substrate bind on an enzyme?
- Allosteric site
- Active site
- Membrane
- Nucleus
Answer: Active site
3. What permanently destroys an enzyme's function at high temperatures?
Answer: Denaturation
Heat disrupts hydrogen and ionic bonds, distorting the active site irreversibly.
Last reviewed: May 2026