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

ltbegt In case of lactose presence
(i) Lactose acts as an inducer which binds to the repressor and forms an inactive repressor .
(ii) The repressor fails to bind to the operator region.
(iii) The RNA polymerase binds to the operator and transcript lac mRNA.
(iv) lac mRNA is polycistronic , i.e., produces all three enzymes , `beta`-galactosidase, permease and transacetyase .
(v)The lac operon is switched on .
In case of lactose absence
(i) When lactose is absent, i gene regulates and produces repressor mRNA which translate repression.
(ii) The repressor protein binds to the operator region of the as a result prevent RNA polymerase to bind to the operon.
(iii) The operon is switched off.