#Question id: 4109

When E. coli is grown on a medium containing a mixture of glucose and lactose, it proliferates with complex kinetics. The bacteria proliferate faster at the beginning than at the end, and there is a lag between these two phases when they virtually stop dividing. Assays of the concentrations of the two sugars in the medium show that glucose falls to very low levels after a few cell doublings, but lactose remains high until near the end of the experimental time course (not shown). Although the concentration of lactose is high throughout most of the experiment, β-galactosidase, which is regulated as part of the Lac operon, is not induced until more than 100 minutes have passed. Choose correct explanation why the Lac operon is not induced by lactose during the rapid initial phase of bacterial proliferation

A. The rapid bacterial growth at the beginning of the experiment results from the metabolism of glucose. The slower growth at the end results from metabolism of lactose.

B. CAP and the Lac repressor mediate induction in the situation

C. The bacteria stopped growing in the middle of the experiment because they ran out of glucose but did not yet possess the enzymes necessary for lactose metabolism

D. Induction of the Lac operon requires that two conditions be met: lactose must be present and glucose must be absent.