# Explain why two different enzymes, such as amylase and lipase, can each only catalyse one type of reaction.

> AQA A-Level Biology (7402) — 3.1.4 Proteins and Enzymes · Explain · 5 marks

> Enzymes are biological catalysts found in living organisms. Amylase catalyses the breakdown of starch, while lipase catalyses the breakdown of lipids. Neither enzyme can catalyse the other's reaction.

## Mark scheme (5 marks)

1. Each enzyme has a specific active site
2. The active site is complementary to only one specific substrate
3. An enzyme-substrate complex forms when the substrate fits the active site
4. Starch cannot fit the active site of lipase (or lipids cannot fit the active site of amylase) because the shapes are not complementary
5. Therefore no enzyme-substrate complex forms and no reaction is catalysed

## Related

- [Revision notes for AQA A-Level Biology (7402)](https://www.gradenine.co.uk/learn)
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