The intercellular or intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GABA-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway.
The “reception” and “conversion” of a “chemical message” (e.g., hormone) by a cell. For example, G-proteins (which are embedded in the surface membrane of certain cells, but extend through to outside and inside of the membrane) accomplish signal transduction. When a hormone, drug, neurotransmitter, or other signal chemical binds to the receptor (on the exterior of the cell membrane), the receptor activates the G-protein, which causes an effector inside cell to produce a “signal” chemical inside cell, which causes the cell to react to the original external chemical signal received.
The process by which a receptor interacts with a ligand at the surface of the cell and then transmits a signal to trigger a series of reactions within that cell.
Biochemical events that conduct the signal of a ligand (e.g., hormone or drug) from the cell exterior, through the cell membrane, and into the cytoplasm. This involves a number of molecules, including receptors and second messengers.
Biochemical conversion that is part of a process, such as the docking of hormone to receptor, stimulating cellular production of specific enzymes or other proteins.