Signaalipolku

Signaalipolku (signal pathway) is a series of molecular interactions by which a cell converts an external signal into a functional response. Signaling pathways begin with a receptor that detects cues such as growth factors, hormones, or environmental stimuli. Activation triggers a transduction cascade that relays and amplifies the signal through intracellular proteins and second messengers, ultimately affecting processes such as gene expression, metabolism, and cytoskeletal organization.

Key components include receptors (for example receptor tyrosine kinases, G protein–coupled receptors, and intracellular receptors), transducers such as kinases and GTPases, second messengers (cAMP, Ca2+, IP3, DAG), and transcription factors. The architecture often features amplification, specificity, integration with other pathways, and feedback mechanisms that modulate the intensity and duration of the response.

Several signaling pathways are central to biology, including the MAPK/ERK pathway, PI3K–Akt pathway, JAK–STAT, Wnt, Notch, and Hedgehog. Signaling pathways govern development, cell growth, differentiation, metabolism, and immune responses. Dysregulation or cross-talk between pathways can contribute to diseases such as cancer, metabolic disorders, and neurodegenerative conditions, making them important targets in medicine. Research in this area combines genetics, biochemistry, live-cell imaging, and computational modeling to map networks and understand cellular decision making.