Name the components of lac operon and discuss their role.

Explanation

An operon is a part of DNA which acts as single regulatory unit having one or more structural genes, an operator gene, promoter gene, regulator gene, a repressor, an inducer or corepressor.
Lac operon model consists of following components
(i) Structural genes These are the fragments of DNA which transcribe mRNA for polypeptide synthesis. Three commonly found structural genes in lac operon are :
z gene which codes for B-galactosidase B-gal), that helps in the hydrolysis of disaccharide into monomeric units, i.e. lactose into galactose and glucose.
y gene which codes for permease, increases the permeability of the cell to `beta-`galactosidase.
a gene which codes for a transacetylase catalyses the transacetylation of the lactose in its active form.
These three structural genes are located in a row adjacent to each other and are linked to each other. They contain the information to determine the sequence of amino acid present in the protein.
(ii) Promoter These are the sequences of DNA where RNA polymerase binds and initiates the transcription of structural genes and controls the rate of mRNA synthesis.
(iii) Operator These are the sequence of DNA lying adjacent to promoter at which specific repressor protein binds, so that it acts as a switch for expression of genes.
(iv) Regulator It is the gene (i gene) which codes for the repressor protein that binds to the operator and suppresses the transcription of genes, thus, switching off the gene.
(v) Inducer It is the substrate which prevents the repressor from binding to the operator. It may be the chemical of diverse nature like metabolite, hormone substrate, etc. Binding of inducer causes the gene to switch on. In case of lacoperon, lactose acts as induce.