AP BIOLOGY

Detailed explanation-1: -Catabolite activator protein (CAP) acts as a glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the “hunger signal” molecule cAMP.

Detailed explanation-2: -Catabolite activator protein (CAP), also known as cyclic AMP receptor protein (CRP), is activated by cyclic AMP and stimulates synthesis of the enzymes that break down non-glucose food molecules. It is composed of two identical subunits, shown here in blue from PDB entry 1cgp .

Detailed explanation-3: -Catabolite repression is positive control of the lac operon. The effect is an increase in the rate of transcription. In this case, the CAP protein is activated by cAMP to bind to the lac operon and facilitate the binding of RNA polymerase to the promoter to transcribe the genes for lactose utilization.

Detailed explanation-4: -The cAMP/CAP complex enhances the reading of DNA by polymerase 50-fold. At the lac operon, the gene expression of lactose degradation and transport enzymes is strongest when lactose or allolactose removes the lac repressor inhibition while the CAP/cAMP complex stimulates the binding of RNA polymerase.

Detailed explanation-5: -Extracellular glucose affects the lactose operon activation by inhibiting the production of cAMP (catabolite repression) and by reducing the efficiency of lactose permease to transport lactose molecules into the cell (inducer exclusion).