E coli cells are growing in a medium containing lactose but

E. coli cells are growing in a medium containing lactose but no glucose. How would a mutation that prevents Lac repressor binding to the operator affect expression of the lac operon?

A)

increase expression of the lac operon

B)

decrease expression of the lac operon

C)

not change expression of the lac operon

Solution

A Control mechanism is a response to glucose, which uses the catabolite activator protein (CAP) homodimer to greatly increase production of -galactosidase in the absence of glucose. Cyclic adenosine monophosphate (cAMP) is a signal molecule whose prevalence is inversely proportional to that of glucose. It binds to the CAP, which in turn allows the CAP to bind to the CAP binding site, which assists the RNAP in binding to the DNA. In the absence of glucose, the cAMP concentration is high and binding of CAP-cAMP to the DNA significantly increases the production of -galactosidase, enabling the cell to hydrolyse lactose and release galactose and glucose. Option A is the correct answer.