Give examples of positive and negative control in the lac operon?

Positive control:


- lactose binding to LacI (repressor), preventing it from binding to the operator, and therefore allowing RNA polymerase to bind to the promotor.


- Absense of glucose allows cAMP to be formed, which binds to CRP. cAMP-CRP binds to the activator binding site which promotes RNA polymerase to bind to the promotor





Negative control:


- In the absense of lactose, LacI (repressor) binds to the operator and prevents RNA polymerase from binding to the promotor, therefore no transcription


- Presence of glucose inhibits the enzyme adenylate cyclase which is involved in the formation of cAMP. Without cAMP-CRP, it does not bind to the activator binding site.