Signal transduction

Signal transduction is the process by which a cell converts an external or internal signal into a specific cellular response, often through molecular interactions that amplify and regulate the signal.

Receptor: A molecule or cellular structure that specifically recognizes and binds another molecule or stimulus. Receptors detect signals and initiate many transduction pathways.
Ligand: A molecule that binds specifically to another molecule, such as a receptor. Many signaling pathways begin when a ligand binds its receptor.
Insulin signaling pathway: The network of intracellular reactions triggered when insulin binds its receptor. It coordinates glucose uptake, metabolism, and growth in response to insulin.
Endocrine signaling: Communication in which hormones travel through circulation to affect distant target cells. It describes a long-distance mode of delivering signals, rather than their intracellular processing.
Crosstalk: Interaction between signaling pathways that allows activity in one pathway to affect another. Crosstalk complicates predictions based on studying pathways in isolation.
Second messenger: A small intracellular molecule or ion that relays signals from receptors to target proteins. Second messengers spread and amplify signals inside the cell.
G protein-coupled receptor: A cell-surface receptor that activates intracellular G proteins in response to extracellular ligands. This receptor family connects many hormones and sensory signals to internal pathways.
MAPK/ERK pathway: A kinase cascade that regulates processes including cell proliferation, differentiation, and survival. It converts growth-factor signals into changes in cellular activity and gene expression.
Paracrine signaling: Cell communication in which released signals act on nearby cells. It distinguishes local signal delivery from the transduction that follows reception.
Biased agonism: The ability of a ligand to favor some signaling outputs of a receptor over others. It challenges the idea that each receptor has one uniform response to activation.

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