Practice question

Tryptophan operon serves biosynthetic anabolic role synthesizing essential amino acid from simple chorismate precursor, consuming substantial energy and nitrogen resources. Regulation as repressible system reflects cellular economy: when intracellular tryptophan abundant through uptake from environment or previous synthesis, further production becomes wasteful and should cease. Operon normally remains transcribed, with trpR gene encoding aporepressor protein that becomes functionally active only after binding tryptophan co-repressor molecule. This architecture contrasts sharply with inducible catabolic operons like lac that remain off by default requiring inducer to remove repression, illustrating logical inversion between degradative and biosynthetic pathway control strategies optimized for growth.