Question

A recent research paper demonstrated that cAMP bound to CAP acts more strongly on the lac operon than on the arabinose operon. Given what you know about catabolite regulation, and the lac operon, list the order of preference of utilisation of the three sugars; arabinose, lactose and glucose.

Answer 1

Glucose inhibits the adenylyl cyclase, enzyme responsible for the conversion of ATP to cAMP.

So in the presence of glucose, cAMP will not be synthesized and cAMP-CAP will not form. So lactose and arabinose will be utilized once glucose is exhausted.

cAMP-CAP helps RNA polymerase binding to the Given that cAMP-CAP complex binds more strongly on the lac operon than on the arabinose operon, it means that RNA polymerase will bind tightly to the lactose as compared to arabinose operon. TIght biding of RNA polymerase increase the chance the expression of the operon. So, lactose will be utilized before arabinose.

So, the sequence of utilization will be glucose, lactose and in the last arabinose.