What happens to gene expression in the TRP operon when the operator is blocked?

When the operator in the TRP operon is blocked, gene expression is inhibited. The TRP operon is responsible for the synthesis of tryptophan in bacteria, and its regulation is a classic example of feedback inhibition. When tryptophan levels are sufficient, the tryptophan will bind to the repressor protein, activating it. The activated repressor then attaches to the operator region of the operon, blocking RNA polymerase from transcribing the genes necessary for tryptophan production.

This blockage effectively prevents the transcription of structural genes involved in the synthesis of tryptophan, which means that no mRNA is produced, and consequently, the proteins coded by these genes are not synthesized. Therefore, the presence of a bound repressor at the operator region directly inhibits gene expression within the operon. This mechanism allows the cell to conserve resources when tryptophan is already present in sufficient quantities.