Biology / Unit 6 Bio 1315 short lesson, about 20 seconds
The trp Operon: Repressible, Negative Regulation
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The idea
The trp operon is repressible: when tryptophan is abundant, it binds a repressor protein that blocks the operon's operator, halting transcription.
In practice
Two tryptophan molecules bind the trp repressor, changing its shape so it can bind the operator and block polymerase.
Where people slip
The trp operon is switched off by tryptophan's presence, not on — abundant tryptophan signals the cell to stop making more.
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