A level Biology B · Edexcel 9BI0 · Topic 1D
Enzymes
Key points
- Enzymes are globular proteins that act as biological catalysts by lowering the activation energy.
- The active site has a specific shape complementary to the substrate. In the induced-fit model it changes shape slightly as the substrate binds, forming an enzyme–substrate complex.
- Rate rises with temperature until the enzyme starts to denature: bonds holding the tertiary structure break and the active site changes shape.
- Each enzyme has an optimum pH; extreme pH disrupts ionic and hydrogen bonds.
- Rate rises with substrate concentration until all active sites are occupied (rate limited by enzyme concentration).
- Competitive inhibitors fit the active site (their effect is reduced by adding more substrate); non-competitive inhibitors bind elsewhere and change the active site's shape.
- Initial rate is found from the gradient of a tangent at time zero.
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Enzymes are globular proteins that act as biological catalysts: they speed up reactions without being used up. Their specificity and sensitivity to conditions follow directly from the shape of the active site.
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