# The lac operon in E. coli is a well-studied example of gene regulation. Describe the role of the lac repressor protein in controlling the expression of the lac genes.

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

## Mark scheme (4 marks)

1. Understanding the lac repressor's role in controlling gene expression
2. Correctly describing the lac repressor's mechanism of action
3. Describing the effect of allolactose on the lac repressor protein
4. Correctly describing the overall effect of the lac repressor protein on lac gene expression

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