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Trp Operon

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Biochemistry 2280A
Eric Ball

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Trp Operon39 Negative regulation example At trp operonIn Ecoli the 5 genes for tryptophan biosynthesis are transcribed from a common promoterIn ecoli 5 genes required for trypophan biosynthesis genes requried to make tryptophan is expressed on same rna and translated form that common rnaThe operon shown EDCBAthey make diff rpotein products which are required for tryp biosynthesis Is trp operon expressed when there is a little or a lot of tryptophan in the cellular environment A little The key here these genes are required for synthesis Cell wants to turn them on when it needs tryptophan when it cant get it from env This occurs when there is very little tryptophan around It would rather use tryptophan from env if it could If it cant it has to make its own tryptophan by turning on the gene Trp operon is ONLY expressed when tryptophan is in medium Between the 35 and 10 sequences is an element called the Trp operator that binds a protein called the Trp repressorWhen tryptophan is low tryptophan dissociates from the Trp repressor The Trp repressor no longer binds the Trp operatorRNAP can access the Trp promoter transcirption occurs trp repressor isnt just a green blob it has structure an dstrucutre relates to its function When no tryp low trypany tryp bound to repressor dissocaites trp repressor no longer binds to operator when it has no longer trytophan bound to it When repressor 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 binds to complex and represses When tryophan repressor bound to operator it blocks rna polymerase from getting into promoter Trp repressor bound at operatorrna polymerase cant get in polymerase want to get intther but it cant sterically inhibts binding of rna polymerase to promoterIn this case no expression Simple and elegant way to regualte gene expression 44 repressor blocking the spot
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