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