# Explain why the tertiary structure of an enzyme is essential for its function, referring to the role of R groups in maintaining this structure.

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

> Enzymes are globular proteins whose specific three-dimensional shape is critical to their activity. The tertiary structure of an enzyme arises from interactions between the R groups of its constituent amino acids.

## Mark scheme (4 marks)

1. The tertiary structure forms the active site, which is complementary in shape to the substrate
2. Named interaction(s) between R groups that maintain tertiary structure
3. If these R group interactions are disrupted, tertiary structure is lost (denaturation) and the active site changes shape
4. Without the complementary active site, the enzyme–substrate complex cannot form and catalysis does not occur

## Key terms

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

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-tertiary-structure-of-d8a80077) · Published by Druglandscape Ltd.