An idea of the complexity of the metabolic networks in cells that contain thousands of different enzymes is given by the figure showing the interactions between just 43 proteins and 40 metabolites to the right: the sequences of genomes provide lists containing anything up to 45,000 genes.[122] However, it is now possible to use this genomic data to reconstruct complete networks of biochemical reactions and produce more holistic mathematical models that may explain and predict their behavior.[123] These models are especially powerful when used to integrate the pathway and metabolite data obtained through classical methods with data on gene expression from proteomic and DNA microarray studies.[124] Using these techniques, a model of human metabolism has now been produced, which will guide future drug discovery and biochemical research.[125] These models are now used in network analysis, to classify human diseases into groups that share common proteins or metabolites.[126][127]