Figure 1. Domains of biological systems described by networksA. Metabolic pathways are typically described as a series of sequential reactions involving small molecules and catalytic enzymes. B. Signaling pathways describe the passage of signaling events, often triggered by a ligand/receptor combination. C. Gene regulatory networks are directed graphs that describe the circuitry of regulatory effects exerted from one gene to another. D. Molecular interaction networks are typically unsigned diagrams that represent uncharacterized interactions between a suite of molecules, often proteins. E. Genetic interactions describe the relationships between genes. Edges here describe the nature of the relationship, as opposed to the mechanisms that are involved in the relationship.