# A mutation occurs in a gene, changing one DNA base to a different base. Explain how this mutation could result in a non-functional protein being produced.

> Edexcel A-Level Biology A: Salters-Nuffield (9BN0) — 1.4 DNA, RNA and protein synthesis · Explain · 5 marks

> Mutations are changes to the sequence of bases in DNA. A point mutation changes a single base in a gene.

## Mark scheme (5 marks)

1. The sequence of bases in DNA codes for the sequence of amino acids in a protein
2. A changed base sequence leads to a different (or wrong) amino acid being incorporated into the protein
3. This results in a different sequence of amino acids (in the polypeptide chain)
4. The protein folds into a different three-dimensional shape / the shape of the protein changes
5. A changed shape means the protein cannot carry out its function (e.g. an enzyme's active site no longer fits its substrate / a structural protein cannot provide support)

## Key terms

- [mutation](https://www.gradenine.co.uk/glossary/mutation)
- [protein](https://www.gradenine.co.uk/glossary/protein)

## Related

- [Revision notes for Edexcel A-Level Biology A: Salters-Nuffield (9BN0)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-mutation-occurs-in-a-gene-e97d7024) · Published by Druglandscape Ltd.