Answer to Question #258909 in Genetics for Juleka

Question

You are interested to study the mutation in the regulatory gene (lach) of a lac operon which significantly alters the shape of repressor protein produced, causing loss of function. By using separate labelled diagrams, describe briefly the actions of the normal and mutated fac operon in absence of lactose.

Answer 1

Lac operon is an inducible operon in which presence of key metabolic substance i.e., lactose induces transcription of structural genes. Lac operon contains three structural genes, z, y and a. Gene-z codes for enzyme β-galactosidase which breaks down lactose into glucose and galactose. Gene-y codes for enzyme β-galactose permease, a membrane-bound carrier protein which helps in transfer of metabolites. Gene-a codes for enzyme β-galactose transacetylase that transfers an acetyl group from acetyl CoA to β-galactosidase.

Regulation of lac operon in absence of inducer-lactose:

Repressor protein is produced by the regulatory i gene. The repressor protein binds to the operator region due to which RNA polymerase cannot proceed with the transcription of structural genes and hence, no enzymes are produced.

Regulation of lac operon in presence of inducer-lactose:

Repressor protein is produced by the regulatory i gene. Inducer i.e. lactose binds to the repressor protein due to which the repressor cannot bind to the operator region. RNA polymerase can thus proceed with the transcription of structural genes and enzymes are produced.