The lac Operon
▪ When Lactose is Absent
i. When lactose is absent, i gene regulates and produces repressor mRNA which translate repression.
ii. The repressor protein binds to the operator region of the operon and as a result prevents RNA polymerase to bind to the operon.
iii. The operon is switched off.
▪ When Lactose is Present
i. Lactose acts as an inducer which binds to the repressor and forms an inactive repressor.
ii. The repressor fails to bind to the operator region.
iii. The RNA polymerase binds to the operator and transcribes lac mRNA.
iv. lac mRNA is polycistronic, i.e., produces all three enzymes, β-galactosidase, permease and transacetylase.
v. The lac operon is switched on.
