Which one of the following statements for the lac operon in E. coli is INCORRECT?​​

Correct option is B

The lac operon is a genetic system in E. coli that controls the metabolism of lactose, and it is regulated by both a repressor protein and an activator protein. The lac operon is regulated based on the presence of lactose and glucose in the environment.

Option 1 (Correct):

The lac operon is indeed controlled by two components:

• Lac repressor: This binds to the operator region of the operon to prevent transcription when lactose is absent.
• CAP (Catabolite Activator Protein): This binds to the promoter when glucose levels are low, promoting the transcription of the lac genes in the presence of lactose.

Option 2 (Incorrect):

The lac operon is highly expressed when lactose is present and glucose is absent, not when both are absent. Glucose inhibits the operon expression via catabolite repression. When glucose is present, even if lactose is available, the operon is not highly expressed because the CAP protein does not bind efficiently to the promoter region.

Option 3 (Correct):

The lac operon is indeed highly expressed when lactose is present (which inactivates the repressor) and glucose is absent (which allows the CAP protein to bind and activate the operon).

Option 4 (Correct):

In the presence of lactose, the lac repressor undergoes a conformational change and cannot bind to the operator, allowing transcription of the lac operon to occur.

Information Booster:

1. Lactose acts as an inducer by binding to the lac repressor, causing it to release from the operator and enabling transcription.
2. Glucose inhibits the lac operon expression through catabolite repression, where cAMP levels are reduced, preventing CAP from binding to the promoter.
3. CAP (Catabolite Activator Protein) enhances transcription of the lac operon when glucose is low and lactose is present.
4. The lac operon is an example of inducible gene expression, where genes are expressed only when needed (in this case, when lactose is available).
5. In the absence of lactose, the lac repressor remains bound to the operator, preventing transcription of the operon.
6. Glucose is the preferred carbon source for E. coli, and the presence of glucose limits the use of lactose.

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