Question

In E.coli, three enzymes B-galactosidase, permease and transacetylase began to be produced as soon as lactose was added. Explain why the enzymes were not forming in the absence of lactose.

Answer 1

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

1) Gene Z will form Beta-galactosidase.

2) Gene Y will form Permease.

3) Gene A will form Transacetylase.

When lactose is not available, the lac repressor binds tightly to the operator preventing transcription by RNA polymerase due to which enzyme are not able to synthesize.