Question

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

Options

• lactose is present and it binds to the repressor.

• repressor binds to operator.

• RNA polymerase binds to the operator.

• lactose is present and it binds to RNA polymerase.

Answer 1

In E.coli, the lac operon gets switched on when lactose is present and it binds to the repressor.

Explanation:

In E. coli, the lac operon is naturally in an “off” state because a repressor protein is bound to the operator, physically blocking RNA polymerase from transcribing the genes. When lactose enters the cell, it is converted into an isomer called allolactose, which acts as an inducer. This inducer binds to the repressor protein, causing it to change shape and release its grip on the operator. With the operator now free, RNA polymerase can bind to the promoter and move forward to transcribe the structural genes necessary for lactose metabolism.