Under what conditions does the trp repressor block transcription of the trp operon?
Question: Under what conditions does the trp repressor block transcription of the trp operon?
The trp operon is a group of genes that are involved in the synthesis of the amino acid tryptophan in bacteria. The expression of these genes is regulated by a mechanism called negative feedback, which means that the end product of the pathway inhibits its own production. In this case, the end product is tryptophan, and it inhibits the transcription of the trp operon by binding to a protein called the trp repressor.
The trp repressor is a protein that can bind to a specific DNA sequence called the operator, which is located between the promoter and the structural genes of the trp operon. When the trp repressor binds to the operator, it blocks the access of RNA polymerase to the promoter, and thus prevents the transcription of the trp operon. However, the trp repressor can only bind to the operator when it is bound to tryptophan. Tryptophan acts as a corepressor, which means that it enhances the binding affinity of the repressor to the operator.
Therefore, under what conditions does the trp repressor block transcription of the trp operon? The answer is when tryptophan levels are high in the cell. When tryptophan is abundant, it binds to the trp repressor and activates it. The activated trp repressor then binds to the operator and shuts down the expression of the trp operon. This way, the cell avoids wasting energy and resources on making more tryptophan than it needs. When tryptophan is scarce, it dissociates from the trp repressor and inactivates it. The inactive trp repressor cannot bind to the operator and allows RNA polymerase to transcribe the trp operon. This way, the cell can produce more tryptophan to meet its demand.
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