Question

Assertion (A): Lac mRNA is synthesized in the presence of inducer.
Reason (R): The activity of repressor protein is suppressed by inducer.

• A. A and R are correct. R is the correct explanation of A.
• B. A and R are correct. R is not the correct explanation of A.
• C. A is correct but R is incorrect.
• D. A is incorrect but R is correct.

Hint:

In the lac operon system, the inducer (lactose or its analog) binds to the repressor, which prevents it from blocking the operator site, thus allowing the genes to be transcribed.

Answer 1

The Correct Option is A

The Lac Operon Model and Role of the Inducer

The Lac operon model explains the regulation of lac genes in bacteria. The inducer (lactose or an analog) plays a crucial role in the transcription of these genes:

• Assertion (A): In the presence of an inducer, the lac operon is turned on, leading to the synthesis of lac mRNA.
  The inducer binds to the repressor, preventing it from binding to the operator, thus allowing RNA polymerase to transcribe the mRNA for lac enzymes.
• Reason (R): The inducer suppresses the activity of the repressor protein.
  Normally, the repressor binds to the operator and blocks transcription, but in the presence of the inducer, the repressor undergoes a conformational change that prevents it from binding to the operator, allowing the genes to be expressed.

Thus, both Assertion (A) and Reason (R) are correct, and R correctly explains A.

Therefore, the correct answer is (1) A and R are correct. R is the correct explanation of A.