Question

In medium where equally was growing lactose was added which induces lac operon then why there is lac operon shut down same time sometime after addition of lactose in medium

Answer 1

The repressor molecule has also affinity for lactose, in the presence of lactose, it leaves the operator free so that transcription takes place. But, when the lactose is completely metabolised and exhausted , the repressor again attaches to the operator and transcription process terminated. and this type of regulation is known as negative regulation.