# Explain why the tertiary structure of an enzyme is essential for its function, and describe one way in which a permanent change to this structure would affect the enzyme's ability to catalyse a reaction.

> OCR A-Level Biology A (H420) — 2.2 Biological molecules · Explain · 4 marks

> Enzymes are globular proteins whose function depends on maintaining a precise three-dimensional shape. Certain environmental conditions or chemical agents can alter this shape irreversibly.

## Mark scheme (4 marks)

1. The tertiary structure determines the shape of the active site
2. The active site is complementary to the substrate, allowing an enzyme-substrate complex to form
3. A permanent change to tertiary structure denatures the enzyme, altering the shape of the active site
4. The enzyme-substrate complex can no longer form, so the rate of reaction decreases to zero / no catalysis occurs

## Key terms

- [tertiary structure](https://www.gradenine.co.uk/glossary/tertiary-structure)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](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-why-the-tertiary-structure-of-0e454fc0) · Published by Druglandscape Ltd.