Transcription of the lacZ and lazY genes of the lac operon begin when?

a. lactose bind to the operator


b. RNA polymerase bind to the lacZ gene


c. the repressor protein binds to the inducer


d. the repressor is release from the promoter


e. lactose bind to RNA polymerase

Transcription of the lacZ and lazY genes of the lac operon begin when?
The lac operon is under control such that it is only expressed when there is no glucose AND there is lactose (or IPTG). Lactose binds to the repressor, preventing it from binding to a site overlapping the RNAp binding site on the promoter.





a - not correct, the repressor, not lactose, binds to the operator


b - not correct, RNAp binds upstream of the operon at the promoter


c - Lactose (or IPTG) is the inducer, which binds to the repressor and inhibits its binding to the operator, so this is it!


d - ... not quite. Repressor binding is transient, the repressor binds and lets go, binds and lets go, etc. But there's a chance your instructor will say this is the answer. :P


e - lactose does not bind RNAp





for an animation illustrating this, see:


http://www.sumanasinc.com/webcontent/ani...





For lots and lots more info, see:


http://en.wikipedia.org/wiki/Lac_operon