题目
题目

APBIO142-030 with labs S19 - CollegeBoard* AP Exam Prep: Multiple Choice

单项选择题

The Trp operon is a coordinately regulated group of genes (trpA–trpE) that are required for tryptophan biosynthesis in E. coli. Based on the figure above, which of the following correctly describes the regulation of the Trp operon?

选项
A.In the absence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.
B.In the presence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.
C.In the absence of tryptophan, the trpR gene is inactive, preventing the production of the repressor that blocks expression of the operon.
D.In the presence of tryptophan, the trpR gene is inactive, preventing the production of the repressor that blocks expression of the operon.
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思路分析
When evaluating regulation of the Trp operon, it's important to connect the presence or absence of tryptophan to whether the repressor is activated to block transcription. Option 1: 'In the absence of tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon.' This is incorrect beca......Login to view full explanation

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When tryptophan concentrations are high in Escherichia coli, what happens?

When arginine binds to the repressor, the repressor does not bind to the operator.  

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