Multiple choice

If the gene encoding the trp repressor is mutated, such that it can no longer bind tryptophan, then will the transcription of the trp operon occur?

  1. Yes, because the trp repressor can only bind the trp operon and block transcriptional initiation when it is bound to tryptophan.

  2. No, because this mutation does not affect the part of the repressor that can bind the operator.

  3. No, because the trp operon is repressed only when tryptophan levels are high.

  4. Yes, because the trp operon can allosterically regulate the enzymes needed to synthesize the amino acid tryptophan.
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A Correct answer
Explanation

If the repressor can no longer bind tryptophan, then it cannot bind the operator and transcription of the trp operon will always be on, whether tryptophan levels in the cell are high or low.

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