Question

Describe the structure and function of Lac operon.

Answer 1

Lac operon:-
(Here lac refers to lactose), a polycistronic structural gene is regulated by a common promoter and regulatory genes. Such arrangement is very common in bacteria and is referred to as operon. The lac operon consists of:
I. One regulatory gene (the $i$ gene - here the term i derived from the word inhibitor) and
II. Three structural genes ($z,y$ and $a$).
Functions:-
1. The $i$ gene codes for the repressor of the lac operon.
2. The $z$ gene codes for beta-galactosidase ($\beta$-gal), which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units, galactose and glucose.
3. The $y$ gene codes for permease, which increases permeability of the cell to p-galactosides.
4. The $a$ gene encodes a transacetylase.
Hence, all the three gene products in lac operon are required for metabolism of lactose. In most other operons as well, the genes present in the operon are needed together to function in the same or related metabolic pathway.