# Explain how competitive and non-competitive inhibition differ in their effects on the kinetics of an enzyme-catalysed reaction, including reference to how increasing substrate concentration affects each type of inhibitor.

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

## Mark scheme (4 marks)

1. Competitive inhibitors bind to the active site, whereas non-competitive inhibitors bind to an allosteric/different site on the enzyme.
2. Increasing substrate concentration can overcome competitive inhibition because substrate outcompetes the inhibitor for the active site, restoring Vmax.
3. Non-competitive inhibition cannot be overcome by increasing substrate concentration because the inhibitor binds at a site other than the active site and is not displaced by substrate.
4. Non-competitive inhibition reduces Vmax (maximum rate of reaction) by reducing the catalytic activity/changing the shape of the active site, whereas apparent Km is increased by competitive inhibition but Vmax is ultimately unchanged.

## Key terms

- [competitive inhibition](https://www.gradenine.co.uk/glossary/competitive-inhibition)
- [non-competitive inhibition](https://www.gradenine.co.uk/glossary/non-competitive-inhibition)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-competitive-and-non-competitive-inhibition-5dc8a370) · Published by Druglandscape Ltd.