Question

In $lac$ operon, repressor protein binds to

• A. Structural gene
• B. Promoter
• C. Regulator gene
• D. Operator

Answer 1

The correct option is D Operator

The lac operon
The lac operon is an inducible operon system that remains usually in a repressed condition and gets activated only when the substance to be metabolised (lactose) is present.
Regulator gene
A lac operon has a regulator gene (lac i). The i gene is responsible for coding the repressor protein of the lac operon.
Operator
Operator is a genetic sequence that lies adjacent downstream to the promoter region of DNA and regulates the synthesis of RNA from the downstream structural genes.
The repressor protein binds to the operator region of DNA and this switches off the lac operon.
Promoter
Promoter is the segment of DNA lying upstream to the operator and provides a site for initial binding of RNA polymerase to proceed with transcription.
Structural gene
A lac operon has three structural genes (lac z, lac y and lac a). The structural genes code for specific enzymes: lac z codes β-galactosidase, lac y codes permease and lac a codes transacetylase.
Final answer
(B) Operator