In the medium where E. coli was growing, lactose was added, which induced the lac operon. Then, why does lac operon shut down some time after addition of lactose in the medium?
The lac operon constitutes of a number of genes, the operator gene, the promoter gene and the regulator gene. The lactose is an inducer and attaches with the repressor and makes it inactive. RNA polymerase attaches with the promoter region resulting in the production of gene products and enzymes. The enzymes metabolize the lactose into glucose and galactose. The level of lactose decreases after breakdown and causes the repressor to be synthesized from the regulator gene. The synthesized repressor attaches to the operator gene and inhibits the action of RNA polymerase from transcription. This stops the transcription making the lac operon to shut down after sometime. Final Answer The repressor binds to the operator when the lactose is removed, thereby making the lactose operon negatively regulated.
