Noise in Biochemical Reaction Networks

At extremely low concentrations, the number of molecules that can participate in a chemical reaction becomes so small that fluctuations (noise) about the mean concentration start to become important. The transcription factor protein (the 'lac repressor') which controls the genes associated with lactose metabolism in E. coli provides a well known example. The lac repressor is active at nanomolar concentrations, for which one can compute there are only of the order ten molecules present in an E. coli cell volume. To understand the effects of fluctuations in biochemical reaction networks, one can solve for the properties of a selection of linear reaction networks (linear networks do not involve bimolecular reactions). The analysis sheds light on how noise is transmitted through detection motifs, and how to 'coarse-grain' reaction networks by the elimination of fast reactions.