Question

The $lac$ operon consists of

• A. One regulatory gene and three structural genes
• B. Two regulatory genes and two structural genes
• C. Three regulatory genes and three structural genes
• D. Four regulatory genes only

Answer 1

The correct option is A One regulatory gene and three structural genes

Operon
Operon is a cluster of structural genes which have a common promoter which get transcribed as a single polycistronic mRNA. Examples of operon include lac operon, trp operon etc.
$lac$ operon
The lac operon is an inducible operon system that remains usually in a repressed condition and gets activated only when the substance to be metabolised (lactose) is present. It consists of polycistronic structural genes having a common promoter and associated regulatory genes.

The three structural genes having a common promoter and operator are lac z, lac y and lac a and one regulatory gene is lac i which has its own promoter.
Final answer
(D) One regulatory gene and three structural genes