Which protein binds to the operator to block transcription in the lac operon?

Which protein binds to the operator to block transcription in the lac operon?

• A. Allolactose
• B. Promoter
• C. Lac repressor
• D. RNA polymerase

Answer: (C)

The Lac repressor is the protein that binds to the operator to block transcription. It sits at the operator region overlapping the promoter, physically preventing RNA polymerase from initiating transcription of the lacZYA genes when lactose isn’t present. When lactose is available, the inducer allolactose binds the repressor, causing it to release from the operator and allowing transcription to proceed. The other components play different roles: allolactose acts as the inducer that disables repression, the promoter is the site where RNA polymerase binds to start transcription, and RNA polymerase is the enzyme that carries out transcription itself.

The Lac repressor is the protein that binds to the operator to block transcription. It sits at the operator region overlapping the promoter, physically preventing RNA polymerase from initiating transcription of the lacZYA genes when lactose isn’t present. When lactose is available, the inducer allolactose binds the repressor, causing it to release from the operator and allowing transcription to proceed. The other components play different roles: allolactose acts as the inducer that disables repression, the promoter is the site where RNA polymerase binds to start transcription, and RNA polymerase is the enzyme that carries out transcription itself.