signal transduction

In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes, activated by second messengers resulting in what is thought of as a "signal trandusction pathway". Such processes are usually rapid, lasting on the order of milliseconds in the case of ion flux, minutes for the activation of protein and lipid mediated kinase cascades, or hours and days in terms of gene expression. In many signal transduction processes, the number of proteins and other molecules participating in these events increases as the process emanates from the initial stimulus, resulting in a "signal cascade" and often results in a relatively small stimulus eliciting a large response. This is referred to as amplification of the signal.
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A complex multistep pathway from the cell membrane through the cytoplasm to the nucleus involved in cell proliferation and differentiation. The components are growth factors, growth factor receptors, membrane and cytoplasmic tyrosine kinases, GTP-binding (G) proteins, nuclear binding proteins and transcription factors.

biochemical event that conducts the "signal" of a hormone or growth factor from the exterior of a cell, through the membrane and into the cytoplasm; involves receptors, ligands, messengers, and other molecules.