How does negative control affect the lac operon in E. coli?

• A. Negative control involves the binding of a repressor protein to the promoter, preventing translation.
• B. Negative control involves the binding of a repressor protein to the operator, preventing transcription.
• C. Negative control involves the binding of an activator protein to the promoter, enhancing transcription.
• D. Negative control involves the removal of a repressor protein from the operator, allowing transcription.

Answer: (B)

Verified step by step guidance

1. Understand the concept of the lac operon: The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It includes structural genes, a promoter, an operator, and regulatory genes.
2. Define negative control: Negative control in gene regulation refers to mechanisms that decrease or inhibit gene expression. This typically involves a repressor protein that binds to the operator region of an operon.
3. Identify the role of the repressor protein: In the lac operon, the repressor protein binds to the operator, a specific DNA sequence, to prevent transcription of the downstream genes. This binding blocks RNA polymerase from transcribing the genes necessary for lactose metabolism.
4. Distinguish between transcription and translation: Transcription is the process of copying a segment of DNA into RNA, while translation is the process of synthesizing proteins from RNA. Negative control affects transcription, not translation.
5. Clarify the effect of removing the repressor: When lactose is present, it binds to the repressor protein, causing it to change shape and release from the operator. This removal allows RNA polymerase to access the promoter and initiate transcription of the lac operon genes.