Fig. 4. Cellular metabolism can be represented as a network. (A) Toy metabolic reaction set. Network description of the reaction set: (B) connecting all metabolites in a single reaction with undirected links; (C) substrates are only connected to products with undirected links; and (D) same as in C with directed links. (E) Bipartite network representation of the reaction set. (F) Network with reactions as nodes, and reactions that share a metabolite as educt–product are connected.