Question

what is lac operon?

Answer 1

Lac operon is a required operon for transportation and metabolism of lactose in Escherichia coli, as in other enteric bacteria. Presents 3 structural adjacent genes: promoter, terminator and operator. Lac operon is regulated by several factors, including glucose and lactose availabilty.

Answer 2

To expand the good answer above a little bit I'd say the three genes which allow the transport and metabolism of lactose are normally repressed unless there is high lactose and low glucose. The lac repressor is released from the control element (Promoter) and the genes can be transcribed.

Answer 3

Not a bad video for explaining the basics of the Operon http://www.dnatube.com/video/22/Lac-operon-mechanism