What determines if the lac operon is active or inactive?

The activity of the lac operon is influenced by multiple factors, including the presence of glucose, the presence of lactose, and the interaction between regulatory proteins and RNA polymerase (RNAP).

Glucose acts as a primary energy source for E. coli, and its presence can inhibit the expression of the lac operon through a phenomenon known as catabolite repression. When glucose is abundant, the bacteria do not need to utilize lactose as an energy source, resulting in reduced expression of the genes required for lactose metabolism.

Lactose, on the other hand, is a crucial inducer for the lac operon. When lactose is present in the environment, it is converted into allolactose, which binds to the lac repressor protein. This binding causes a conformational change in the repressor, preventing it from binding to the operator region of the operon, thereby allowing RNAP to access the promoter and initiate transcription of the downstream genes necessary for lactose utilization.

Additionally, the competition between the repressor protein and RNAP is a key regulatory mechanism. The repressor, when bound to the operator, physically blocks RNAP from transcribing the operon. The presence of allolactose competes with the repressor for binding,