Tryptophan Operon in E. Coli.

 ᐒ trp Operon in E. Coli.

What is triptophan Operon? write about triptophan Operon in E. Coli.



Rep[ressible operon(Tryptophan or trp operon) is switch off when a chemical substances called co-repressor is present. Tryptophan or trp operon of E.coli is an example of repressible operon. The trp operon model in E.coli has following components- 

1. Structural Gene: The E.coli synthesises tryptophan from a precursor molecule in a series of 5 steps, each catalised by a specific enzyme. 5 genes code for these enzymes. These genes transcribe mRNAs which are translated to polypeptide & latter they function as enzyme. The tryptophan operon comprises 5 structural gene denoted as trp E, trpD, trpB, trpA that are too together on a
chromosome acting together as one transcriptional unit. Thus single on=off switch can control them all.


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2.
Operator gene: It controls a specific series of structural genes & lies adjacent to them. It remains turned on till it is joint by the aporeceptor protein produced by the regulator gene. Therefore, the cisterns keep functioning, producing enzymes. The later catalised the synthesise of tryptophan of the rho-material.


3.
Promoter gene: It lies adjacent to operator & each the site where the RNA polymerase enzyme binds. When the
operator gene is turned on, this enzyme moves on the operator gene & structural gene & enzyme.


Lac Operon



4.
Regulatory Gene(trpR): It control the operator gene in corporation with corepressor. The corepressor may be end product of metabolic accumulated in excess in the cell or receive by the cell from outside. The regulator gene cods for a protein named aporepressor. The later combines with corepressor & the complex acts as a repressor & joins the operator gene which is turned off. The structural gene now stop transcription & enzyme synthesis end.



Mechanism of Repressor: When the enzyme are required, the operon corresponding to an amino acid is expressed.
         When the amino acid tryptophan is in abundant aupply, the biosynthetic enzyme are no longer neede feedback repression. The responsible operon generally function in the anabolic pathway.



Co-Repressor: It is a non protein compound which may come fromn outside or from metabolic within the cell. For
trp operon the co-repressor is tryptophan.

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