Question

Regarding the assertion and reason, select the correct answer.
Assertion [A]: Lac operon of E.coli is a type of ‘inducible’ operon.
Reason [R]: Lac operon normally remains ‘switched off’, and functions only when the host (whose gut harbours the E.coli) consumes milk.

• A. Both A and R are true and R explains A
• B. Both A and R are true, but R does not explain A
• C. A is true and R is false
• D. Both A and R are false

Answer 1

The correct option is A Both A and R are true and R explains A

The lac operon of E.coli typically stays in the ‘off’ position. When the host organism consumes milk, lactose becomes available in his gut, and the lac operon of E.coli gets to work to digest this lactose. The lactose molecules bind to the repressor and modify it in such a way that the repressor cannot bind to the operator. As a result, RNA polymerase can freely bind to the promoter and initiate transcription of the structural genes. This ultimately leads to the formation of the proteinaceous enzymes responsible to digest lactose. When there is no lactose available in the gut, transcription need not happen, and the repressor manages this. Since this operon can get switched on just in times of need, it is known as ‘inducible operon’.