Answer:
An operon consists of sets of genes that are part of single transcription unit and is under the control of a single promoter. Lac operon is found in E.coli which consists of three structural genes which code for beta-galactosidase, permease, and transacetylase.
These genes are under the control of one promoter which is present upstream of these structural genes. The role of promoter is that it provide the binding site for RNA so that the RNA polymerase can start the transcription of these structural genes.
Between structural gene and promoter, operator region is present which when binds to repressor protein then it prevents the binding of RNA polymerase to the promoter and stops the transcription initiation.
