Gene Regulatory Networks

Tryptophan is one of the 20 amino acids that link together to form proteins. For humans it is an essential amino acid, we must get it from our diet since we cannot synthesize it. E. coli bacterial cells, however, can synthesize the amino acid tryptophan when it is not provided from the environment (e.g. the gut where it lives). It would be wasteful to synthesize tryptophan when it is readily available in the environment so E. coli have evolved a genetic switch (the trp operon) that turns off synthesis in this case and turns on synthesis when tryptophan is no longer present in the environment. The following model is based loosely on the control of tryptophan production by the trp operon. Although the trp gene codes for 5 enzymes that act on five substrates, or precursors, we simplify it a bit by considering only one of each. Our treatment follows Banks and Mahaffy [2], who considered a general negative feedback genetic control model. Their model, hence ours too, does not include transcriptional attenuation of the trp operon. See Santillan and Mackey [11] for a more realistic model of the trp operon. Our references contain further related material. Check the web page http://science.nhmccd.edu/biol/operon/ton.html for an animated description of the trp operon.