Inducible operon is a type of operon which is expressed in the presence of an effector molecule called inducer.
An inducer is a small molecule that binds to a regulatory protein to stimulate gene transcription.
Inducible operon generally functions in catabolic pathway.
Lac operon is an example of inducible operon, in which, lactose and its analog lead to express lac genes that are inducers.
This operon has following components:
Structural genes: used in transcription to produce mRNA that later on synthesize protein molecule by the process called translation. Lac operon of E. coli has three structural genes: Z, Y and A, which are required for the breakdown of glucose.
Operator genes: control the specific function of structural genes. When the operator gene is turned on by inducer, it expresses cistron. But cistron doesn’t express when the gene is turned off by repressor.
Promoter gene: situated adjacent to operator gene.
It has two functions:
(a) Promoter gene marks the site on DNA where the RNA polymerase enzyme binds,
(b) the base sequence of the promoter gene determines the template strand for mRNA transcript.
Regulator gene: controls the operator gene when inducer is present in the cytoplasm of the cell. It is adjacent to the operator gene which it controls. This gene codes the controlling gene and produce repressor, which binds to the gene which requires control.
Repressor: is a protein molecule produced by regulator gene to control transcription of mRNA.
Inducer: is a chemical that inactivate repressor, and induce the movement of RNA polymerase from promoter to structural gene.