Select the correct statements from the following :

a- The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene.

b- The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.

c- In the presence of an inducer, such as lactose or allolactose, the repressor is activated by interaction with the inducer.

d- Regulation of lac operon by repressor is referred to as positive regulation.

a and b .

The correct answer is Option (3) –a and b .

The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon.

In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds.

Essentially, regulation of lac operon can also be visualised as regulation of enzyme synthesis by its substrate. Remember, glucose or galactose cannot act as inducers for lac operon.

Regulation of lac operon by repressor is referred to as negative regulation.