Final answer:
Diauxic growth is the bacterial use of one carbon source followed by another after depletion of the first. cAMP and CAP are essential in this process; as glucose depletes, cAMP-CAP complex binds to operon promoters, activating genes necessary for metabolism of an alternative sugar like lactose.
Step-by-step explanation:
Diauxic growth is a pattern of bacterial growth in which a bacterium first consumes one carbon source and then, after depletion of this first preferred source, shifts to metabolize a secondary carbon source. This phenomenon involves a lag phase where the bacterium adapts its metabolic machinery to utilize the second substrate, resulting in a biphasic growth curve.
During this process, cyclic AMP (cAMP) and the catabolite activator protein (CAP) play crucial roles. When glucose, the preferred carbon source, is scarce, cAMP levels rise in the cell. The increased cAMP binds to CAP, creating a cAMP-CAP complex. This complex then binds to promoter regions of operons, like the lac operon, which control the processing of alternative sugars like lactose. The cAMP-CAP complex enhances the binding ability of RNA polymerase to the promoter, resulting in increased transcription of the genes necessary for the metabolism of the alternative sugar.
In the presence of glucose, however, CAP is inactive, and cAMP levels are low, preventing the formation of the cAMP-CAP complex. Therefore, genes for the metabolism of alternative sugars are not activated until glucose levels become low.