Which molecule serves as the corepressor in the lac operon by binding to the repressor?

Which molecule serves as the corepressor in the lac operon by binding to the repressor?

• A. LacI repressor
• B. Operator protein
• C. Repressor
• D. Lac 1 protein

Answer: (D)

In lac operon regulation, a small molecule modulates the activity of the repressor. The repressor protein (LacI) binds to the operator and blocks transcription when lactose is absent. When lactose appears, it is converted to allolactose, which binds to LacI and changes its shape so it can no longer bind the operator. This releases the block and allows transcription to proceed. Allolactose acts as an inducer in this system, not a corepressor. A corepressor is something that enhances repressor binding, which is not how the lac operon is regulated. None of the listed options correctly name the molecule that binds to the repressor; the actual signal is allolactose.

In lac operon regulation, a small molecule modulates the activity of the repressor. The repressor protein (LacI) binds to the operator and blocks transcription when lactose is absent. When lactose appears, it is converted to allolactose, which binds to LacI and changes its shape so it can no longer bind the operator. This releases the block and allows transcription to proceed. Allolactose acts as an inducer in this system, not a corepressor. A corepressor is something that enhances repressor binding, which is not how the lac operon is regulated. None of the listed options correctly name the molecule that binds to the repressor; the actual signal is allolactose.