In Negative operon : -
- cAMP has negative effect on lac operon
- Co-repressor binds with inducer
- Co-repressor binds with repressor
- Co-repressor does not bind with repressor
Answer
(3) Co-repressor binds with repressor
Solution
In a negatively controlled operon, the repressor protein switches the operon off by binding to the operator.
In a repressible operon (e.g. tryptophan operon) the repressor made by the regulator gene is inactive by itself. The end product (e.g. tryptophan) acts as a co-repressor: it binds with the repressor and makes it active, and the active repressor–co-repressor complex then binds to the operator and stops transcription.
cAMP (with CAP) has a positive effect on the lac operon, so option (1) is wrong.
∴ Co-repressor binds with repressor.
Answer: (3)