# Explain how covalent modification of an enzyme can regulate its activity, using phosphorylation as an example.

> IB DP Biology Higher Level (2023 syllabus) — C1.1 Enzymes and metabolism · Explain · 4 marks

## Mark scheme (4 marks)

1. Covalent modification involves the addition or removal of a chemical group to/from an enzyme, changing its activity
2. Phosphorylation involves the transfer of a phosphate group from ATP to a specific amino acid residue (e.g. serine, threonine, or tyrosine) on the enzyme, catalysed by a protein kinase
3. Addition of the phosphate group changes the shape of the enzyme's active site / tertiary structure, either activating or inhibiting the enzyme
4. The modification is reversible because a phosphatase enzyme can remove the phosphate group, restoring the original enzyme conformation and allowing rapid regulation of metabolic pathways

## Key terms

- [covalent modification](https://www.gradenine.co.uk/glossary/covalent-modification)
- [phosphorylation](https://www.gradenine.co.uk/glossary/phosphorylation)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](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-how-covalent-modification-of-an-131a534a) · Published by Druglandscape Ltd.