# Explain why an enzyme can be described as a biological catalyst, and explain how the 'lock and key' hypothesis accounts for enzyme specificity.

> WJEC A-Level Biology (Wales) — 1.4 Biological reactions and enzymes · Explain · 5 marks

> Enzymes are proteins made from chains of amino acids. They are found in all living cells and are essential for controlling metabolic reactions.

## Mark scheme (5 marks)

1. An enzyme speeds up the rate of a chemical reaction
2. The enzyme is not used up / not permanently changed by the reaction and can be reused
3. Each enzyme has an active site with a specific / unique shape
4. The substrate has a complementary shape to the active site, allowing only that substrate to fit / form an enzyme-substrate complex
5. Because the active site shape is specific, the enzyme cannot act on other substrates / other substrates cannot fit the active site

## Key terms

- [biological catalyst](https://www.gradenine.co.uk/glossary/biological-catalyst)
- [enzyme specificity](https://www.gradenine.co.uk/glossary/enzyme-specificity)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](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-why-an-enzyme-can-be-ff697e81) · Published by Druglandscape Ltd.