In E.coli, the lac operon gets switched on when :

Options

A. Lactose is present and it binds to the repressor.
B. Repressor binds to operator.
C. RNA polymerase binds to the operator.
D. Lactose is present and it binds to RNA polymerase.

Answer

A

Explanation

If the preferred carbon source is absent and lactose is provided in the growth medium of the bacteria, then the lactose gets transported into the cells by the action of the enzyme permease. This induces the operon and the following events takes place.
1. The presence of the induçer such as lactose or allolactose, inactivates the repressor due to interaction between inducer with repres sor (ie., binding of inducer to repressor). As a result, the inactive repressor fails to bind to the operator region.
2. This results in RNA polymerase to access the promoter and the transcription then proceeds further and lac mRNA is formed which is polycistronic and produces all three enzymes -`beta`-galactosidase, permease and transacetylase. Thus, the operon gets switched on.