AP BIOLOGY

Detailed explanation-1: -Glucose absent, lac tose present: Strong transcription of the lac operon occurs. The lac repressor is released from the operator because the inducer (allolactose) is present. cAMP levels are high because glucose is absent, so CAP is active and bound to the DNA.

Detailed explanation-2: -Importantly, this process is affected by glucose levels, because cAMP levels are decreased in the presence of glucose catabolites. Thus, an elevation in cAMP concentration signals the absence of glucose, because lower glucose levels lead to increased cAMP levels.

Detailed explanation-3: -Glucose is thought to reduce cAMP level by decreasing the phosphorylated form of enzyme IIAGlc, which is proposed to be involved in the activation of adenylate cyclase (3–5). Glucose also is known to reduce the CRP level through the autoregulation of the crp gene (7–10).

Detailed explanation-4: -In the presence of glucose circulating cAMP levels are very low and consequently the initiation of transcription from the lac operon is very low. As glucose levels decrease the concentration of cAMP increases activating CAP which in turn binds to the CAP site stimulating transcription.

Detailed explanation-5: -In the absence of both glucose and lactose, transcription is turned off. Because the glucose levels are low, cAMP will be high. Hence, CAP will be active in this condition and will bind to DNA.