PCB 3063 Lecture Notes - Lecture 17: Biomolecular Structure, Aptamer, Essential Amino Acid
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Lecture 17: the tryptophan operon is a repressible gene system, remember that an inducible system is one that is normally off that can be induced to be turned on. The regulatory region is upstream of the structural genes, and everything is controlled by the operator. Recall an operator is a promoter than controls a whole operon: when there is no tryptophan around, so transcription occurs and nothing repressors the site. However, if there is lots of tryptophan in the environment, the tryptophan itself will bind to the repressor and prevent transcription. It binds to an allosteric site on the repressor, and then the repressor can bind to the repressor gene which prevents transcription: post transcriptional regulation is also possible. This is done by conformational changes in the mrna: attenuator sites are leader sequences that are transcribed even when the operon is repressed.