In detail

Gene regulation by end product repression

on the example of tryptophan (trp-operon)

End-product repression is based on the Operon model of Jacob and Monod.
If there is no tryptophan in the cell in the prokaryote E. coli, the repressor is inactive and the transcription leads to the synthesis of the proteins trpE, trpD, trpC, trpB and trpA and thus an increase in the concentration of tryptophan.
The tryptophan provides itself again for an inhibition of its synthesis (negative feedback), because it binds to the repressor and activates it. This stops the transcription for the synthesis of tryptophan again.
No tryptophan: Transcription is expiring. Enzymes that synthesize tryptophan are synthesized. (Repressor inactive)
With tryptophan: The formed tryptophan binds to the repressor and changes its structure (repressor active). Transcription for the synthesis of tryptophan is stopped.