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 are namely `beta `-galactosidase, `beta`-galactosidase or Lactose permease and B-galactoside transacetylase. These are produced by Z, Yand A genes respectively. Enzyme RNA polymerase enzyme initiates the synthesis of these 3 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 as 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.