Question

What acts as an inducer in lac operon ? How does it switch on the operon ?

Answer 1

Lactose is known as inducer because it controls switching on and switching off of operon.

Switch on condition:-

When lactose is added in the culture medium of E.coli, Lactose enters in E.coli. Lactose behaves as an inducer and repressor bind to lactose. When repressor bound to lactose, it undergoes conformational change due to which it's a binding site to operator undergo change and repressor leave operator. Now the operator is free. RNA polymerase moves over structural genes and transcribed polycistronic mRNA which translates three enzymes :

1) Beta-galactosidase from gene Z.

2) Permease from gene Y.

3) Transacetylase from A.