Observe the given picture and answer the following questions.
At which region of the operon does the repressor protein bind and prevent RNA polymerase from transcribing the operon?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Operator region
The figure states that the repressor binds to the operator region (o) and prevents RNA polymerase from transcribing the operon. In the upper part of the figure (in absence of inducer) the repressor sits on the box marked o, which lies between the promoter (p) and the structural gene z.
Option (1) Promoter region — Incorrect. The promoter is the site where RNA polymerase itself binds to start transcription. The repressor does not sit on the promoter; it blocks the polymerase from the operator next to it.
Option (2) Operator region — Correct. The operator lies next to the promoter. When the repressor is bound to it, RNA polymerase cannot transcribe the structural genes z, y and a.
Option (4) Structural genes — Incorrect. The structural genes z, y and a code for beta-galactosidase, permease and transacetylase. They are the part that gets transcribed, not the binding site of the repressor.