CBSE Class 12-science Answered

Jacob and Monod (1961) explained that the enzymes β-galactosidase, lac permease and transacetylase are required for lactose catabolism. The DNA segments which code these enzymes are lac Z, lacY and lac A. These are called structural genes and are located in a linear sequence in the bacterial chromosome.

Mechanism of the lac operon

• In the absence of inducer lactose, the regulator gene R produces a repressor protein which binds to the operator site and prevents transcription of structural genes.
• When inducer lactose is introduced in the medium, it binds to the repressor and prevents it from binding to the operator. The operator then induces the RNA polymerase to bind to the promoter and transcribe mRNA by the structural genes and enzymes. produced.
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