Study the schematic representation of the genes involved in the lac operon given below and answer the questions that follow :
`{:(p,i,p,o,z,y,a):}`
(a) Identify and name the regulatory gene in this operon. Explain its role in 'switching off' the operon.
(b) Why is the lac operon's regulation referred to as negative regulation ?
(c ) Name the inducer molecule and the products of the genes 'z' and 'y' of the operon. Write the functions of these gene products.

Explanation

The Operon model was provided by Jacob and Monad in 1961.
(a) Regulatory gene in the lac operon is 'I' gene code for the repressor protein in lac operon. Repressor protein is DNA binding protein, which binds at operator 'o' region of the lac operon and inhibits the transcription of the lac operon.
(b) Lac operon's regulation is referred to as negative regulation because in presence of an inducer (1, 6-allolactose) repressor is inactivated and allows RNA polymerase access to promotor and transcripton proceeds.
(c ) The inducer molecule is 1, 6-allolactose (isomer of lactose).
gene-z - `beta`-galactosidase.
gene-y - permease.
Function :
`beta`-galaclosidase : It hydrolyse the `beta`-galactoside bond between lactose to give galactose and glucose.
Permease : It increases the permeability of the cell to `beta`-galactosides.