Question

Describe the regulation of the trp operon in the presence of tryptophan and in the absence of tryptophan. Name all components involved and tell where they bind.

Answer 1

The trp operon is regulated by the availability of tryptophan; it's active and produces tryptophan when the amino acid is absent, and is repressed when tryptophan is abundant by binding of the tryptophan-repressor complex to the operator, blocking transcription.

Step-by-step explanation:

The regulation of the trp operon varies depending on the presence of tryptophan within the cell. In the absence of tryptophan, the repressor protein does not bind to the operator, allowing RNA polymerase to transcribe the genes required for tryptophan synthesis. The trp operon is therefore active, and the cell synthesizes tryptophan.

However, when tryptophan is abundant, it acts as a corepressor by binding to the trp repressor. This activated complex can then bind to the operator, inhibiting RNA polymerase binding, and thus, the transcription of the trp operon is stopped. This effectively reduces the production of more tryptophan when it is not needed, showcasing a negative feedback loop.

The trp operon includes the promoter, the operator, and the coding region, which makes up the five structural genes necessary for tryptophan biosynthesis. The repressor protein and tryptophan molecules are the key components involved in its regulation, demonstrating a classic example of gene expression control in prokaryotic cells.