# Explain why a mutation in the promoter region of a gene may result in a non-functional protein being produced at a lower than normal rate, even though the coding sequence of the gene is 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 genes and influence the rate at which RNA polymerase initiates transcription. Mutations can affect any region of a gene, including regulatory sequences upstream of the coding region.

## Mark scheme (4 marks)

1. The promoter is the region where RNA polymerase binds to initiate transcription
2. A mutation in the promoter alters the base sequence, reducing the ability of RNA polymerase (or transcription factors) to bind
3. Less / reduced transcription occurs, so less mRNA is produced
4. Less mRNA means less translation occurs, so less protein is produced; the protein itself is non-functional because the coding sequence is unaltered but production rate is reduced

## Key terms

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

## 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-cd192703) · Published by Druglandscape Ltd.