Question

In the medium where


e.coli was growing ,loctose was added ,which induced the lac operan.then why does lac operan shut down some time after addition of lactose in the medium?

Answer 1

This particular phenomenon is known as negative regulation. It takes place in Lac operon which is itself an inducer (the part of a molecule which disables the repressors and also expresses a particular gene) which sticks to the repressor and inactivates its function.
Once the lactose has fixed itself to the repressor the RNA polymerase binds to the promoter region (which starts off the transcription of a specific gene as seen in 3' and 5' end strands they are located 5' end strand).
To make it more simpler, the repressor binds to the operator gene and prevents the RNA polymerase to transcribe (lit. write a code in the gene to initiate a process of transcription) which stops the Lac operon and shuts it down or stops the three main expressors promoter, operator and the regulator gene after the addition of lactose to the lac medium.