# Explain why the tertiary structure of an enzyme is essential for its function, referring to the role of bonds that maintain this structure.

> OCR A-Level Biology A (H420) — 2.2 Biological molecules · Explain · 4 marks

> Enzymes are globular proteins whose function depends on the precise three-dimensional shape of their active site. This shape is determined by the tertiary structure of the polypeptide chain.

## Mark scheme (4 marks)

1. The tertiary structure creates a specifically shaped active site that is complementary to the substrate
2. Named bond(s) that maintain tertiary structure — at least one of: hydrogen bonds, disulfide bonds, ionic bonds, hydrophobic interactions
3. If these bonds are disrupted (e.g. by heat or pH change) the tertiary structure is altered / lost (denaturation)
4. Altered tertiary structure means the active site is no longer complementary to the substrate, so enzyme–substrate complexes cannot form and catalysis cannot occur

## Key terms

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

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-tertiary-structure-of-05e21554) · Published by Druglandscape Ltd.