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Trp Operon

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Western University
Biochemistry 2288A
Chris Brandl

Trp Operon39 Negative regulation exampleAt trp operonIn Ecoli the 5 genes for tryptophan biosynthesis are transcribed from a commonpromoter In ecoli 5 genes required for trypophan biosynthesis genes requried to maketryptophan is expressed on same rna and translated form that common rna The operon shown EDCBAthey make diff rpotein products which are required fortryp biosynthesis Is trp operon expressed when there is a little or a lot of tryptophan in the cellularenvironmentA littleThe key here these genes are required for synthesis Cell wants to turn them onwhen it needs tryptophan when it cant get it from env This occurs when there isvery little tryptophan around It would rather use tryptophan from env if it could Ifit cant it has to make its own tryptophan by turning on the gene Trp operon isONLY expressed when tryptophan is in medium Between the 35 and 10 sequencesis an element called the Trp operator that binds a protein called the Trp repressor When tryptophan is low tryptophan dissociates from the Trp repressorThe Trp repressor no longer binds the Trp operator RNAP can access the Trp promoter transcirption occurstrp repressor isnt just a green blob it has structure an dstrucutre relates to itsfunction When no tryp low trypany tryp bound to repressor dissocaites trp repressor nolonger binds to operator when it has no longer trytophan bound to it Whenrepressor isnt bound to dna rna plyease can get in and can get transcrpition Sterically inhibits binding No expression in this case If you got tryp around it bindsto complex and repressesWhen tryophan repressor bound to operator it blocks rna polymerase from gettinginto promoter Trp repressor bound at operatorrna polymerase cant get inpolymerase want to get intther but it cant sterically inhibts binding of rnapolymerase to promoter In this case no expression Simple and elegant way to regualte gene expression 44repressor blocking the spot
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