If E. coli bacteria are grown in the presence of lactose:

• A. The repressor will bind the operator allowing transcription of the lac operon genes.
• B. The repressor will not bind the operator preventing transcription of the lac operon genes.
• C. The repressor will not bind the operator allowing transcription of the lac operon genes.
• D. The repressor will bind the operator preventing transcription of the lac operon genes.

Answer: (C)

Verified step by step guidance

1. Understand the role of the lac operon in E. coli: The lac operon is a set of genes responsible for the metabolism of lactose in E. coli. It includes genes that code for enzymes like β-galactosidase, which breaks down lactose into glucose and galactose.
2. Identify the function of the repressor protein: The lac repressor is a protein that binds to the operator region of the lac operon, preventing transcription when lactose is absent. This ensures that the enzymes for lactose metabolism are not produced unnecessarily.
3. Recognize the effect of lactose on the repressor: When lactose is present, it acts as an inducer by binding to the repressor protein. This binding changes the shape of the repressor, preventing it from attaching to the operator region.
4. Determine the outcome of lactose presence: With the repressor unable to bind to the operator, RNA polymerase can access the promoter region and initiate transcription of the lac operon genes, leading to the production of enzymes needed for lactose metabolism.
5. Conclude the correct statement: Given the presence of lactose, the repressor will not bind the operator, allowing transcription of the lac operon genes. This is the mechanism by which E. coli can efficiently utilize lactose when it is available.