# Explain why a mutation in a gene encoding a transcription factor protein could affect the expression of many other genes simultaneously.

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

> Transcription factors are proteins that bind to specific regulatory DNA sequences and influence the transcription of target genes. A single transcription factor may have binding sites on the regulatory regions of multiple genes across the genome.

## Mark scheme (4 marks)

1. Transcription factors bind to specific regulatory/promoter regions of DNA to influence transcription
2. A mutation in the transcription factor gene changes the amino acid sequence / tertiary structure of the transcription factor protein
3. The altered transcription factor can no longer bind correctly to its target regulatory sequences, so transcription of target genes is affected (reduced/prevented/increased)
4. Because the same transcription factor regulates multiple genes (has binding sites on many genes), a single mutation affects expression of all those target genes simultaneously

## Key terms

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

## 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-a-c83c04b0) · Published by Druglandscape Ltd.