# A mutation occurs in the promoter region of a gene coding for an enzyme involved in melanin production. As a result, the gene is transcribed at a much higher rate than normal, leading to excess melanin deposition in skin cells. Explain how a mutation in the promoter region, rather than in the coding sequence of the gene, could lead to increased enzyme production.

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

> Melanin is a pigment synthesised through a series of enzyme-catalysed reactions. The gene encoding one of these enzymes contains a promoter region upstream of the coding sequence. In a particular individual, a base substitution mutation has occurred within the promoter region of this gene.

## Mark scheme (4 marks)

1. The promoter region is the site where RNA polymerase binds to initiate transcription
2. The mutation alters the base sequence of the promoter, increasing the affinity of RNA polymerase for that region
3. Greater / more frequent binding of RNA polymerase leads to increased transcription of the gene, producing more mRNA
4. More mRNA is translated at ribosomes, producing a greater quantity of the enzyme

## Key terms

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

## 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/a-mutation-occurs-in-the-promoter-c4dd9bca) · Published by Druglandscape Ltd.