Signal Transduction Pathways

Signal Transduction Pathways

Signal transduction is the process by which a cell converts an external stimulus into an internal response. An extracellular signaling molecule — a hormone, growth factor, or neurotransmitter — binds a specific receptor at the plasma membrane (e.g., a GPCR or a receptor tyrosine kinase), and the receptor transmits that information inward through second messengers such as cAMP, Ca 2+ , and IP 3 , and through phosphorylation cascades. Because each activated protein can catalyze many downstream reactions, these cascades act as amplifiers: a handful of ligand molecules at the surface can produce a large, coordinated change in gene expression, metabolism, or cell division. The canonical cascades you will encounter in pharmacology include the Ras–Raf–MEK–ERK (MAPK) pathway controlling proliferation, the PI3K–Akt pathway controlling