# Enzymes are proteins that act as biological catalysts. Explain why an enzyme stops working when the temperature is raised significantly above its optimum, referring to the structure of the protein.

> WJEC A-Level Chemistry (Wales) — 4.7 Amino acids, peptides and proteins · Explain · 5 marks

> Enzymes are proteins found in all living organisms. Each enzyme has an active site with a specific shape that allows it to bind to its substrate. At temperatures well above the optimum, the enzyme no longer functions.

## Mark scheme (5 marks)

1. The enzyme is denatured (at high temperature)
2. The bonds holding the protein's three-dimensional shape are broken
3. The three-dimensional shape of the protein changes / the active site changes shape
4. The substrate can no longer fit into / bind to the active site
5. So the enzyme can no longer catalyse the reaction

## Key terms

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

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Source: [GradeNine](https://www.gradenine.co.uk/q/enzymes-are-proteins-that-act-as-c31e41ee) · Published by Druglandscape Ltd.