# Explain why two different enzymes, such as amylase and lipase, cannot catalyse each other's reactions.

> Edexcel GCSE Biology (1BI0) — 1.4 Enzymes · Explain · 4 marks

> Amylase is an enzyme that breaks down starch, while lipase is an enzyme that breaks down lipids. Each enzyme can only catalyse one type of reaction.

## Mark scheme (4 marks)

1. Enzymes have an active site with a specific shape
2. The substrate must be complementary to / fit the active site
3. Starch/the substrate of amylase cannot fit the active site of lipase (or vice versa)
4. Therefore no enzyme–substrate complex is formed so the reaction cannot be catalysed

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