Explain working of Lac-operon with diagrammatic representation.

Explanation

Regulation of gene action is well studied in E.coli bacteria with regard to utilization of lactose by the bacteria .
Utilisation of lactose in E.coli needs three enzymes namely B- galactosidase , B- galactosidase permease and B-galactosidase transacetylase. These are produced by Z,y and a genes respectively . Enzyme RNA polymerase enzymes.
The mechanism of lac-operon can be studied under two steps namely ,
(a) Switched OFF mechanism :When lactose is absent in the medium , the regulator gene produces repressor protein which binds with operator gene . This prevents the movement of RNA polymerase on the structural genes is blocked so there is no synthesis of mRNA from the structural genes Z,Y and a , so there is no synthesis of enzymes . This is called switched OFF mechanism
(b) Switched ON mechanism : When lactose is added to the culture medium . some of its molecules enter into the bacterial cell and one of them , binds itself with repressor . It induces the repressor protein to undergo structural change and makes it inactive . This inactive repressor becomes detached from the operator region . Now the RNA polymerase moves along the DNA and a result the structural genes Z, Y and a produce mRNA . This mRNA synthesises 3 enzymes which are necessary for lactose metabolism . This is called switched ON mechanism .