in the medium where E.Coli was growing , lactose was added, which induced the lac operon .then why the lac operon shut down some time after addition of lactose in the medium?

Asked by pramodtalukdar | 27th Oct, 2016, 09:00: PM

Expert Answer:


Lac operon is regulated by the presence of lactose in the growing medium. 

When Lactose is present in the medium, it binds to the repressor molecule. This prevents the repressor molecule from binding to the operator region of the operon and thus RNA Polymerase can bind to the operator region and transcribe the genes. 


After some time, the levels of lactose in the medium decrease as the cells use up all of the lactose in it. In the absence of lactose the repressor molecule is free and can bind to the operator region again, thus preventing the transcription of the genes, and shutting down the operon. 

Answered by Aniket Vyawahare | 28th Oct, 2016, 11:53: AM