Regulation of genes#2. Operon

"In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter."

.......says wikipedia.
Yeah, so operon is like genes are not likely to be goofing around cells, instead they build up and be placed in order. You will find these things in biology very much. (such as transcription factory)

Lets see some operons

-The lac operon 

this is the lac operon of E.coli.
lac-z codes b-galatosidase, lac-Y is permease, lac-A is acetyl transferase.
each one of them is an enzyme. the last one is not yet identified in cell mechanism.
the galactosidase makes lactose into glucose and galactose.

-The Trp operon

another operon of E.coli
trp E,D,C,B,A each takes small part to from trp

* The way operon functions
Type 1: Activated by activator
Type 2: Activated by loss of repressor

    Type2-1: Inducible operon 유도성 오페론ex: lac
the regulatory gene lacI codes activated repressor, so if there is no allolactose to deactivate the protein, Lac operon gets inhibitied

    Type2-2:repressible operon 억제성 오페론ex: trp
the regulatory gene trpR codes deactivated repressor, so if there is no trp to activate the repressor, then the operon will continue its anablolic reaction to make trp.
So, it makes trp a negative feedback control

* one thing that campbell didn't tell ya
trp operon can be controlled by a mechanism called attenuator.
since E.coli is prokaryotic the RNA is forms continuous hairpin structures while transcripted. There are 4 parts of mRNA that contributes to this hairpin structure.
1-2,2-3 hairpin loop is not that strong but 3-4 hairpin loop is strong so it can stop transription
Case 1) sufficient Trp
the ribosome continues to region2, so 3-4 hairpin loop is made so transcription stops
Case 2) Trp insufficient
it lacks 3-4hairpin loops so transcription continues.