# Explain how competitive inhibitors affect enzyme activity, including the effect of increasing substrate concentration on the degree of inhibition.

> IB DP Biology Standard Level (2023 syllabus) — C1.1 Enzymes and metabolism · Explain · 4 marks

## Mark scheme (4 marks)

1. A competitive inhibitor has a similar shape/complementary shape to the substrate and binds to the active site of the enzyme.
2. The inhibitor prevents the substrate from binding to the active site, so fewer enzyme–substrate complexes form and the rate of reaction decreases.
3. Binding of a competitive inhibitor is reversible, so the inhibitor can dissociate from the active site.
4. Increasing substrate concentration reduces the effect of competitive inhibition because substrate molecules outcompete the inhibitor for the active site, restoring the rate of reaction.

## Key terms

- [competitive inhibitor](https://www.gradenine.co.uk/glossary/competitive-inhibitor)
- [substrate concentration](https://www.gradenine.co.uk/glossary/substrate-concentration)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](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-competitive-inhibitors-affect-enzyme-47b2aaa1) · Published by Druglandscape Ltd.