In the lac operon, glucose also plays an important role along with lactose. When Lactose is present in the environment along with glucose then it cannot deactivate the regulator gene [repressor], as a result, the repressor will bind to the operator and the transcription will be blocked.
When Lactose is present in the environment without glucose then the Catabolite repressor protein will bind to the CAP Site, and lactose will bind to the repressor [regulatory gene product], as a result, the repressor gets deactivated and the transcription takes place.
Lac operon: It is a set of three structural genes z, y, and a which are all transcribed and regulated under one single promoter. The three genes code for β-galactosidase, lactose permease, and transacetylase respectively.
β-galactosidase is responsible for breaking the lactose into glucose and galactose, lactose permease is responsible for transporting lactose across the cell membrane and transacetylase attaches a particular chemical group to target molecules.
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