# Explain how post-translational modifications can alter the function of a protein after it has been synthesised on a ribosome.

> IB DP Biology Higher Level (2023 syllabus) — B1.2 Proteins · Explain · 4 marks

## Mark scheme (4 marks)

1. Post-translational modifications involve chemical changes to a polypeptide after translation is complete
2. Named example of a post-translational modification, e.g. phosphorylation, glycosylation, cleavage of a signal peptide/pro-sequence, acetylation, ubiquitination
3. The modification changes the three-dimensional conformation / active site / binding site of the protein
4. This change in structure alters or activates the protein's function, with a specific consequence stated, e.g. enzyme activation/inactivation, targeting to an organelle, cell signalling, protein degradation

## Key terms

- [post-translational modification](https://www.gradenine.co.uk/glossary/post-translational-modification)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-post-translational-modifications-can-alter-654651d0) · Published by Druglandscape Ltd.