Describe Lac operon concept with labelled sketch.

Explanation

It is an inducible operon, where lactase is the inducer, it is the substrate for the enzyme B- galactasidase the Lac - operon has three stractural gene
Gene Z codes for B- galactosidase enzyme which brakes lactose into galactose and glucose
Gene Y codes for permease which increase the permeability of the cell to lactose
Gene A codes for transacetylase, that catalyses the transacetylation of lactose in active form
When lactose is absent, the gene regulates and produces repressor mRNA which produces the repressor protein. This protein binds to the operator region of the operòn and as a result prevents RNA polymerase to bind to the operon, the operon is switched off.
When lactose is present, it acts as an inducer which binds to the repressor and form an inactive repressor, it fails to bind to operator gene, the RNA polymerase binds to the polycistronie structural gene, it produces all the enzymes B- galactosidase, permease and transacetylase, the lac operon is switched on.