The trp Operon: Repressible, Negative Regulation
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State
The trp operon is repressible: when tryptophan is abundant, it binds a repressor protein that blocks the operon's operator, halting transcription.
Show
Two tryptophan molecules bind the trp repressor, changing its shape so it can bind the operator and block polymerase.
Watch for
The trp operon is switched off by tryptophan's presence, not on — abundant tryptophan signals the cell to stop making more.