Q. Lactose (Lac) Operon is regulated by :
(a) Lac repressor only
(b) Lac repressor and CAP-cGMP complex
(c) Lac repressor and CAP-cAMP complex
(d) CAP-cAMP and CAP-cGMP complex
Solution :
Correct option : C The lac operon (lactose operon) is an operon required for the transport and metabolism of lactose in Escherichia coli and many other bacteria. It contains genes involved in lactose metabolism. It is expressed only when lactose is present and glucose is absent .Two regulators turn the operon “on” and “off” in response to lactose and glucose levels: the lac repressor and catabolite activator protein (CAP). 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. So, the correct option is C.
