EVERYDAY SCIENCE

Detailed explanation-1: -The lac operon of E. coli contains genes involved in lactose metabolism. It’s 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).

Detailed explanation-2: -If lactose and glucose are present, the cell will use all of the glucose before the lac operon is turned on. This type of control is termed catabolite repression. To prevent lactose metabolism, a second level of control of gene expression exists. The promoter of the lac operon has two binding sites.

Detailed explanation-3: -The Lactose operon expresses as long as the Lactose is present. When all lactose is converted into glucose and galactose, the reaction stops.

Detailed explanation-4: -The correct answer is e. The lac operon is usually turned on in the presence of lactose. The lac operon contains genes that are involved in breaking down the sugar lactose. Under most conditions, the operon is turned off by a repressor that binds to the operator and blocks transcription.

Detailed explanation-5: -In lac operon, lactose acts as an inducer. If lactose is provided in the medium for the bacteria, the regulatory gene is activated. The inducer will bind to the repressor protein and render it inactive which allows transcription of the operon. Thus, the lac operon is negatively regulated in this case.