pathways

Pathways are sequences of actions, steps, or reactions that connect an initial state to a subsequent outcome. The term is used across disciplines to describe routes, processes, or networks that enable progression, transformation, or transport. Pathways provide a framework for understanding how complex systems move from one condition to another.

In biology, a pathway describes ordered biochemical or signaling events within cells and organisms. Broad categories include metabolic pathways, which convert substrates into products through enzyme-catalyzed steps; signaling pathways, which relay information to control cellular responses; and developmental or gene regulatory pathways that govern cell fate and tissue patterning. Pathways are characterized by their topology, regulation, and context-dependent activity.

Examples include glycolysis and the citric acid cycle as metabolic pathways; signaling pathways such as MAPK/ERK and PI3K/AKT; and developmental pathways like Notch, Wnt, and Hedgehog. Pathways often exhibit modular organization, feedback control, cross-talk with other pathways, and redundancy to ensure robustness under varying conditions.

In biomedical research, pathway analysis maps experimental data to known pathways to interpret omics results and identify potential drug targets. Key resources include pathway databases such as KEGG, Reactome, and BioCyc, which provide reaction networks and functional annotations.

Beyond biology, the term also refers to routes in transportation and geography, and to educational or career pathways that describe typical routes of progression from training to employment. Across contexts, pathways emphasize connectivity, sequence, and the transfer of information or material from source to destination.