trp operon

Inducible vs. Repressible Systems

My EK biology instructor said we should know these. The lac operon is an example of an inducible protein and the trp operon is an example of a repressible protein.

The trp operon is a repressible system. The primary difference between repressible and inducible systems is the result that occurs when the effector molecule binds to the repressor. With inducible systems, the binding of the effector molecule to the repressor greatly reduces the affinity of the repressor for the operator, the repressor is released and transcription proceeds. The lac operon is an example of an inducible system. With repressible systems, the binding of the effector molecule to the repressor greatly increases the affinity of repressor for the operator and the repressor binds and stops transcription. Thus, for the trp operon , the addition of tryptophan (the effector molecule) to the E. coli environment shuts off the system because the repressors binds at the operator.

Inducible system - the effector molecule interacts with the repressor protein such that it can not bind to the operator

Repressible system - the effector molecule interacts with the repressor protein such that it can bind to the operator