# Explain why a protease enzyme cannot break down starch.

> Cambridge International IGCSE Biology (0610) — 5.1 Enzymes · Explain · 4 marks

## Mark scheme (4 marks)

1. Each enzyme has a specifically shaped active site
2. The shape of the active site is complementary to its substrate (protein), not to starch
3. Starch cannot bind to / enter the active site of protease
4. Therefore no enzyme-substrate complex can form, so starch is not broken down

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