What occurs during tryptophan binding to the repressor?

Tryptophan binding to the repressor protein induces a significant conformational change in the repressor. This change is crucial because it allows the repressor to bind to the operator region of the associated DNA, thereby inhibiting the transcription of genes involved in tryptophan biosynthesis. Essentially, when tryptophan levels are sufficient, its binding to the repressor enhances the repressor's ability to attach to the operator and block RNA polymerase from transcribing the DNA into messenger RNA. This mechanism is part of a feedback inhibition system that maintains cellular homeostasis by regulating the levels of tryptophan in the cell.

In contrast, the activation of RNA polymerase and the synthesis of tryptophan are not directly related to the binding of tryptophan to the repressor; in fact, the opposite occurs: transcription is prevented when tryptophan is present. Thus, the focus is on how the binding of tryptophan modifies the structure of the repressor, highlighting the importance of feedback regulation in gene expression.