Question

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

Answer 1

Hint: Lac Operon by E. Coli includes genes involved in the metabolism of lactose. Only when lactose is present and glucose is absent is it conveyed. As a lactose regulator, the lac repressor works. In response to the levels of lactose and glucose, two regulators transform the operon on and off: the lac repressor and catabolite activator protein.

Complete answer:
It usually prevents the transcription of the operon, but when lactose is present, it stops functioning as a repressor. Via its isomer, allolactose, the lac repressor detects lactose indirectly. As a glucose sensor, catabolite activator protein (CAP) functions. It activates the operon transcription, but only when the level of glucose is low. Indirectly, via the "hunger warning" molecule cAMP, CAP detects glucose. Glucose requires less steps and less energy than lactose to break down. However, if the only available sugar is lactose, the E. Coli is going to go straight forward, using it as an energy source. Bacteria must express the lac operon genes, which encode essential enzymes for lactose uptake and metabolism, in order to use lactose.

These proteins bind to the lac operon's DNA and control its transcription based on the levels of lactose and glucose. Let's take a look at how it works like this. The lac operon also includes a variety of sequences of regulatory DNA. These are DNA regions to which unique regulatory proteins, regulating the operon's transcription, can bind. A negative regulatory site bound by the protein of the lac repressor is the operator. The operator overlaps with the promoter, and RNA polymerase does not bind to the promoter and start transcription when the lac repressor is bound.

Hence, the correct answer is option (C).

Note: Allolactose is an example of an inducer, a tiny molecule that induces a gene or operon to express itself. In the presence of the inducer allolactose, the lac operon is called an inducible operon since it is normally switched off, but can be switched on.