# Explain why the tertiary structure of an enzyme is essential for its function, and describe what happens to this structure when the enzyme is exposed to a high concentration of heavy metal ions.

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

> Enzymes are globular proteins whose catalytic activity depends entirely on maintaining a precise three-dimensional shape. Industrial processes sometimes expose biological systems to heavy metal ions such as lead or mercury, which are known to disrupt protein structure.

## Mark scheme (4 marks)

1. The tertiary structure creates the specific shape of the active site, which is complementary to the substrate
2. Tertiary structure is maintained by bonds between R groups, including hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic interactions
3. Heavy metal ions disrupt / break the bonds maintaining tertiary structure, causing the enzyme to denature
4. The active site changes shape so it is no longer complementary to the substrate, and the enzyme cannot catalyse the reaction

## Key terms

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

## 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-41c24bc2) · Published by Druglandscape Ltd.