KCET · BIOLOGY · STD 12 - 5. Molecular Basis of Inheritance

When does lac operon in E.coli become "switched on "?

A Repressor binds to operator.
B RNA polymerase binds to operator
C Lactose is present, and it binds to the repressor.
D Lactose is present, and it binds to RNA polymerase.

Verified Solution

Answer & Solution

Correct Answer

(C) Lactose is present, and it binds to the repressor.

Step-by-step Solution

Detailed explanation

(C) Lactose is present, and it binds to the repressor.,
The lac operon is an example of an inducible operon which induces transcription of structural genes in the presence of lactose hence it is called an inducer.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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