In E.coli, there enzymes galactosidase, permease and transacetylase are produced in the presence of lactose. Explain why the enzymes are not synthesized in the absence of lactose.

Explanation

When lactose is present in E.coli, it acts as inducer of lactose metabolism. The repressor is inactivated by interaction with inducer such as lactose. This allows RNA polumerase to bind to the promoter site and transcribe the operon to produce lac mRNA. This enables the formation of all the three enzymes for lactose metabolism.
If lactose is not present as inducer, the synthesis of the three enzymes will not take place.