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LS4 Week8Quiz

LS4 Week8Quiz - trp repressor must first bind to a molecule...

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Question Completion Status: Questi on 1 10 points Sav e The trp operon in E. coli encodes enzymes necessary for the biosynthesis of tryptophan. The general mechanism for controlling the trp operon is similar to that observed with the lac operon: when the repressor binds to the operator transcription is prevented; when the repressor does not bind the operator, transcription proceeds. The regulation of the trp operon differs from the regulation of the lac operon in the following way: the enzymes encoded by the trp operon are not synthesized when tryptophan is present but rather when it is absent. In the trp operon the repressor has 2 binding sites: one for DNA and the other for tryptophan. The
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Unformatted text preview: trp repressor must first bind to a molecule of tryptophan before it can bind effectively to the trp operator. The trpR gene encodes the repressor. trpO is the operator. trpA encodes the enzyme tryptophan synthetase. A trpR-repressor cannot bind tryptophan. A trpO-operator cannot be bound by the repressor. And the enzyme encoded by trpA-mutant is completely inactive. Do you expect to find active tryptophan synthesetase in each of the following strains when the cells are grown in the presence of tryptophan and in its absence? (+) indicates wild type. R + O + A + R-O + A + / R + O + A-R + O- A + / R + O + A-R + O- A + / R + O- A-R-O + A + s fi n d tr y...
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