# Explain why a mutation in the promoter region of a structural gene may prevent the production of the encoded protein, even though the coding sequence of the gene remains unchanged.

> OCR A-Level Biology A (H420) — 6.1 Cellular control · Explain · 4 marks

> Transcription factors are proteins that bind to specific DNA sequences near a gene to regulate its expression. The promoter region is a non-coding sequence located upstream of a structural gene.

## Mark scheme (4 marks)

1. RNA polymerase cannot bind to the promoter region
2. Transcription of the gene does not occur / is prevented
3. Transcription factors cannot bind to the mutated promoter
4. Without transcription, no mRNA is available for translation, so the polypeptide / protein is not synthesised

## Key terms

- [promoter region](https://www.gradenine.co.uk/glossary/promoter-region)
- [structural gene](https://www.gradenine.co.uk/glossary/structural-gene)

## 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-a-mutation-in-the-167acc5c) · Published by Druglandscape Ltd.