The various components of lac operon are regulator gene, promoter gene, operator gene and structural genes. Regulatory genes synthesise a chemical called repressor which combine with operator gene to switch off the operon. In the presence of inducer – the lactose, repressor binds with lactose to free the operator gene and the operon is switch on. Promoter gene is the recognition site for RNA polymerase when the operon is switched on. The RNA polymerase pass over the operator gene and reach structural genes to transcribe them. Operator gene controls the expression of operon by switching on and off the structural genes transcribe polycistronic zn-RNA. Lac operon has three structural genes Z, Y and A. The polycistronic m-RNA produces three enzymes galactosidase permease (early of lactose into bacterium), β-galactosidase (breakage of lactose into glucose and galactosidase) and galactoside acetylase (transfer acetyl group to β-galactosidase).
Note : Inducer is a chemical generally a substrate binds with repressor to free the operator ‘ gene.
