Inducible Operon vs Repressible Operon

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Inducible Operon vs Repressible Operon

Genetic regulation is a process where certain proteins and other kinds

of stimuli tend to cause a cell to express genes or not express them.

The bacteria cell system is small system, but it carries out a lot of

activities and must do so economically and efficiently, therefore

actions of these genes must be regulated. There are two types of

regulatory systems: inducible and repressible

An operon is a cluster of genes that work together to form a

polycistronic mRNA. It consists of structural genes, a promoter

region, an operator region, and a regulatory gene. Structural genes

code for the enzymes themselves. RNA polymerase transcribes all of the

genes into a polycistronic mRNA. The promoter is the site where the

RNA polymerase binds to the DNA prior to beginning transcription. The

operator serves as the binding site for the protein called the

repressor. The regulatory gene encodes the repressor protein.

An inducible operon is an operon in which the presence of a key

metabolic substance induces transcription of the structural genes. One

example of an inducible operon is lac operon and the inducer of this

operon is lactose.

A repressible operon is an operon which always transcribes structural

genes unless a repressor is present. One example of a repressible

operon is trp operon and the co-repressor of this operon is


Both lac operon and trp operon have similarities and differences


1. Both lac operon and trp operon have structural genes with related

function are controlled by a single promoter/operator.

2. Both lac operon and trp operon have negative control regulation

system controlled by repressor. There is a regulatory gene in the

operon which encodes the repressor protein that attach to the operator

to prevent transcription.


1. In term of structure, the lac operon has three structural genes:

lacZ, lacY, and lacA. Whereas the trp operon has five structural

genes: trpE, trpD, trpC trpB and trpA.

2. In term of function, an inducible operon is generally involves in

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