LIFE SCIENCE

Detailed explanation-1: -Glucose must be unavailable: When glucose is unavailable, cAMP binds to CAP, making CAP able to bind DNA. Bound CAP helps RNA polymerase attach to the lac operon promoter. Lactose must be available: If lactose is available, the lac repressor will be released from the operator (by binding of allolactose ).

Detailed explanation-2: -However, in the absence of glucose, the lac operon can be activated if the lac i repressor is turned off by lactose binding. More specifically, in E. coli, the switch from glucose use to lactose use depends on the presence of both cAMP and a molecule called catabolite activator protein (CAP).