Define an operon,give an example,and explain an inducible operon.

(N/A) An operon is a functional unit of $DNA$ in bacteria that consists of a cluster of genes under the control of a single promoter. These genes are transcribed together into a single polycistronic mRNA molecule. Examples include the $lac$ operon,$trp$ operon,$ara$ operon,$his$ operon,and $val$ operon.
An inducible operon is a system that is usually turned 'off' but can be switched 'on' in the presence of a specific molecule called an inducer. The $lac$ operon is a classic example of an inducible operon.
The $lac$ operon consists of one regulatory gene (the $i$ gene,which codes for a repressor protein) and three structural genes ($z$,$y$,and $a$).
$1$. In the absence of an inducer (lactose),the repressor protein binds to the operator region $(o)$,preventing $RNA$ polymerase from transcribing the structural genes.
$2$. In the presence of an inducer (allolactose),the inducer binds to the repressor protein,rendering it inactive. The inactive repressor cannot bind to the operator,allowing $RNA$ polymerase to transcribe the structural genes ($z$,$y$,and $a$).
The $z$ gene codes for $\beta$-galactosidase,which hydrolyzes lactose into glucose and galactose. The $y$ gene codes for permease,which increases the cell's permeability to $\beta$-galactosides. The $a$ gene encodes transacetylase.