Question

What would happen to the lac operon in the absence of allolactose?

Answer 1

Lac operon:

Lac operon is the inducible operon in which the presence of various key metabolic substances i.e., lactose induces transcription of structural genes.

1. Lac operon also contains 3 structural genes, z, y, and a.
2. Gene-z codes for the enzyme β-galactosidase that breaks down lactose in glucose and galactose.
3. Gene y codes for the enzyme β-galactose permease, which is a membrane-bound carrier protein that helps in the transfer of metabolites.
4. Gene-a codes for enzyme β-galactose transacetylase which transfers an acetyl group from acetyl CoA to β-galactosidase.
5. Regulation of the lac operon in absence of inducer-lactose/allolactose:
   1. Repressor protein is produced by the regulatory i gene.
   2. 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.
6. Regulation of the lac operon in the presence of inducer-lactose/allolactose:
   1. Repressor protein is also produced by the regulatory i gene. Inducer i.e. lactose binds to repressor protein due to which the repressor cannot bind to operator region.
   2. RNA polymerase can thus proceed with transcription of the structural genes and enzymes are produced.