Respuesta :
Answer:
In prokaryotes like E.coli, the structural proteins with related function are located in a single transcriptional unit called operon.
Explanation:
All the genes within a promoter are under the control of single promoter i.e they are controlled simultaneously. Usually the product of all the structural genes within a operon are needed at the same time.
There is a regulatory region in the operon which include promoter region and the regions where transcription factors binds. RNA polymerase binds to the promoter region for transcribing the structural genes.
In lac operon, there are three structural genes : lacZ - encodes for beta galactosidase, lacY - encodes for permease and lacA - encodes for trans-acetylase.
Repressor is a transcription factor which binds to the regulatory region called operator. Operator lies between the promoter and the transcription start site. Binding of repressor to the operator site blocks the RNA polymerase from transcribing the structural genes.
Inducer is also a regulatory molecule which can activate or repress the transcription. It does so by binding to activator and repressor. In lac operon allolactose serves as inducer. When allolactose binds to repressor, it prevents its binding to the operator site and thus RNA polymerase successfully transcribes the structural genes.
