Cell signal transduction. Computer illustration of signal transduction in an animal cell. Signal transduction occurs when a molecule from outside the cell (orange), for example a hormone molecule, activates a specific receptor located on the cell surface or inside the cell. This receptor triggers a biochemical chain of events inside the cell, creating a response. Depending on the cell, the response may be a change in the cell's metabolism, shape, gene expression, or ability to divide. The signal can be amplified at any stage, so that one signalling molecule can cause many responses.