Explain working of Lac-operon with diagrammatic representation.

Explanation

Working of Lac operon
This concept is proposed by Jacob and monad.
Ecoli cells require 3 enzymes for lactose metabolism.
These enzymes transport and breakdown lactose into galactose and glucose for energy release.
These three enzymes are:
(B-glactosidase, Permease, transacetylase)
As long as glucose is present and lactose is absent in the medium, three enzymes are not produced:
But, with in minutes of adding lactose to the medium, the 3 enzymes are produced in large number.
this concept can be explained under two headings.
1. In the absence of inducer (Lac-operon switched off) The regulatory gene (i) produces the repressor protein which binds to the operator gene when Lactose is absent in the medium.
This prevents transcription because the presence of the repressor prevents the enzyme m-RNA polymerase from binding to the promoter, It results in activation of the structural genes. So that the transcription and translation is stopped and no enzymes are produced. Now the structural genes are said to be switched off.

2. Lacoperon switched on (in presence of inducer) In the presence of Lactose as an inducer interacts and inactivates repressor protein. This repressor protein unable to bind to the operator gene. So that Lac operon is switched on. Then operator gene signals the structural genes to produce polycistronic m-RNA which inturn produces 3 enzymes necessary for lactose metabolism.