# Enzymes are proteins that act as biological catalysts. Explain why an enzyme stops working when it is heated to a very high temperature, referring to the structure of proteins in your answer.

> Eduqas A-Level Chemistry — 4.7 Amino acids, peptides and proteins · Explain · 5 marks

## Mark scheme (5 marks)

1. Proteins have a specific three-dimensional shape / folded structure
2. High temperature breaks the bonds that hold the protein in its shape
3. The protein / enzyme becomes denatured (shape is permanently changed)
4. The active site changes shape so the substrate can no longer fit / bind
5. Therefore the enzyme can no longer catalyse the reaction

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/enzymes-are-proteins-that-act-as-6ade7004) · Published by Druglandscape Ltd.