# Explain how non-competitive inhibitors reduce the rate of an enzyme-catalysed reaction.

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

## Mark scheme (4 marks)

1. A non-competitive inhibitor binds to a site on the enzyme other than the active site (an allosteric site).
2. Binding of the inhibitor changes the tertiary structure / shape of the enzyme, including the active site.
3. The altered active site can no longer bind substrate effectively / the enzyme–substrate complex cannot form (or forms less readily).
4. The rate of reaction is reduced and cannot be restored by increasing substrate concentration (unlike competitive inhibition).

## Key terms

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

## 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-non-competitive-inhibitors-reduce-the-07a82c7b) · Published by Druglandscape Ltd.