# Explain how a change in pH away from the optimum affects the ability of an enzyme to break down its substrate. Include reference to the active site in your answer.

> Eduqas A-Level Biology — 1.1 Chemical elements and biological molecules · Explain · 5 marks

## Mark scheme (5 marks)

1. Enzymes have an optimum pH at which the active site has the correct/complementary shape for the substrate
2. As pH moves away from the optimum, the shape of the active site begins to change
3. The substrate can no longer fit into the active site / the active site is no longer complementary to the substrate
4. No enzyme-substrate complexes can form
5. This is called denaturation / the enzyme is denatured, so the rate of reaction decreases

## Key terms

- [active site](https://www.gradenine.co.uk/glossary/active-site)

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-a-change-in-ph-b1e6232f) · Published by Druglandscape Ltd.