# Amylase is an enzyme that breaks down starch into simple sugars. Explain how the 'lock and key' hypothesis describes the way amylase acts on starch, and explain why amylase cannot break down proteins.

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

## Mark scheme (5 marks)

1. The active site of amylase has a specific shape
2. The starch molecule (substrate) has a complementary shape to the active site
3. Starch enters the active site to form an enzyme-substrate complex
4. Proteins do not have a complementary shape to the active site of amylase
5. Therefore no enzyme-substrate complex can form between amylase and protein, so the protein cannot be broken down

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