Question

Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow.

a) Identify and name the regulatory gene in this operon. Explain its role in ‘switching off the operon.

b) Why is operon`s regulation referred to as negative regulation?

c) Name the inducer molecule and the products of the genes V and of the operon. Write the function of these gene products.

Answer 1

(a) Regulatory gene in this operon is i gene.
Role of the regulatory gene in switching off operon is as follows:
(1) Regulatory gene codes for the repressor protein of the operon, which is synthesized in constant amounts.
(2) The repressor has an affinity for the operator gene. It
binds to the operator and prevents the RNA polymerase from transcribing the structural genes.
(b) When repressor binds to the operator, the operon is switched off and transcription is stopped. So, it is called a negative regulation.
(c) Lactose is an inducer molecule.
Gene ‘z’ codes for beta-galactosidase, which is responsible for the hydrolysis of lactose into galactose and glucose, y gene codes for permease. It increases the permeability of the cell to lactose.