Signal transduction

Signal transduction occurs when an extracellular signaling molecule activates a specific receptor located on the cell surface or inside the cell. In turn, this receptor triggers a biochemical chain of events inside the cell, eventually eliciting a response. Depending on the cell, the response may alter the cell's metabolism, shape, gene expression, or ability to divide. The signal can be amplified at any step. Thus, one signaling molecule can generate a response involving hundreds to millions of molecules.