# Proteases and lipases are enzymes found in the digestive system. Explain how the structure of an enzyme allows it to act as a biological catalyst, and why a protease cannot break down lipids.

> Eduqas A-Level Biology — 1.4 Biological reactions and enzymes · Explain · 5 marks

## Mark scheme (5 marks)

1. Enzymes are proteins made of chains of amino acids that fold to form a specific shape
2. Each enzyme has an active site with a specific/complementary shape to its substrate
3. The substrate fits into the active site to form an enzyme-substrate complex, and the product is released
4. The enzyme is not changed by the reaction and can be reused, acting as a catalyst
5. A protease cannot break down lipids because the lipid molecule does not have a complementary shape to the active site of the protease / enzyme specificity means each enzyme only acts on one specific substrate

## Key terms

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

## Related

- [Revision notes for Eduqas A-Level Biology](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/proteases-and-lipases-are-enzymes-found-b7c883b4) · Published by Druglandscape Ltd.