Lac Operon – Negatively Controlled Inducible Operon
Lac operon is an operon required for the transport and metabolism of lactose in E. coli and some other enteric bacteria. Francois Jacob and Jacques Monod studied gene expression and formulated an operon model.
It consist of 3 adjacent structural genes, a promoter, an operator, a regulator and a terminator. It is regulated by several factors including the availability of glucose and lactose. (An operon is cluster of genes together under a single operon)
It is a negatively controlled inducible operon of gene regulation in prokaryotes because here binding of repressor inhibits transcription.
In simple terms, lac operon is off when lactose is absent and is switched on when lactose is present in the environment.
Structural genes: codes for enzymes. Structural gene of an operon usually lie adjacent to one another and RNA polymerase moves from one structural gene to the next, transcribing all of the genes into a single mRNA which is translated into enzymes.
This operon has three structure genes: lacA, lacY and lacZ
Promoter (lacP) : is the site where RNA polymerase binds to DNA to begin transcription.
Operator (lac O): resides adjacent to promoter and it serve as binding site for repressor (a gene regulatory protein which is like an off switch)
Inhibitory gene: lac i which codes for repressor protein.
00:23 introduction of operon system in prokaryotes
06:26 Lac operon in detail
12:02 Mechanism
Do you want to know what happens if glucose and lactose both are present in the environment? Check out Catabolite Repression – Positive Control of Lac Operon here.