LAC OPERON

 It is the amount of lactose present in a bacterial cell .

It consist two condition 

I - Switch on condition 

When lactose amount is less in bacterial cell .

RNA polymerase binds to promoter to initiate expression .

Regulatory gene synthesis repressor protein . This protein comes and binds to operator region . 

Asa result confirmation of operator changes and it blocks RNA polymerase to move forward .

Transcription and translation cannot takes place so no enzyme formation in cell .

This condition is known as switch off condition .

II - Switch on condition 

When lactose quantity increase in the cell .

Some of the lactose come and bind to repressor protein .As a result protein confirmation  changes .

Due to change is confirmation operators get unblocked .

RNA polymerase moves forward and transcription and translation occur .

structure genes lac A synthesis transacetylase lac Y  permease and lac Z galactosidase .

This condition is known as switch on condition.