FRANCIS LEROY & MATHILDE VANSPEYBROUCK, BIOCOSMOS / SCIENCE PHOTO LIBRARY FRANCIS LEROY & MATHILDE VANSPEYBROUCK, BIOCOSMOS / SCIENCE PHOTO LIBRARY
Animation showing the repression of the tryptophan (trp) operon, the set of genes that code for the amino acid tryptophan in Escherichia coli bacteria. When there is a plentiful supply of tryptophan in the environment the bacterium's resources are better placed synthesising other compounds and so the trp operon is silenced. The gene that codes for the repressor (red, top left) is transcribed to mRNA (messenger ribonucleic acid, light blue) and then translated to the inactive form of the protein. When tryptophan (yellow) is present it binds the tryptophan repressor (purple), activating it. This allows it to bind to the trp operon operator (red, top centre). This stops the enzyme RNA polymerase (blue oval) from binding to the operator and initiating transcription of the operon.
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