Question

What is the role of glucose in catabolite repression? What is the role of glucose in catabolite repression?

It stimulates transcription from the lac operon, causing an increase in cAMP levels in the cell.
It increases the levels of cAMP in the cell, stimulating transcription from the lac operon.
It represses transcription from the lac operon, causing a decrease in cAMP levels in the cell.
It decreases the levels of cAMP in the cell, repressing transcription from the lac operon.

Answer 1

It decreases the levels of cAMP in the cell, repressing transcription from the lac operon.

Step-by-step explanation:

When glucose is absent, cAMP serves as coactivator binds to CRP, the catabolite gene activator protein. The CRP-cAMP complex binds to the site near the lac promoter and stimulates the expression of the operon by RNA polymerase many folds.

Catabolite repression refers to inhibition of the synthesis of enzymes of lactose catabolism when glucose is present as an energy source. In the presence of glucose, synthesis of cAMP is inhibited resulting in its lower cellular concentration. The lower cAMP levels do not allow the binding of cAMP and CRP. The result is reduced expressed of lac operon.