G-protein signal transduction. Animation of the process involved in signal transduction involving G-proteins. Signal transduction is when an extracellular response can trigger a biochemical chain of events inside a cell. In this example, an inactive G protein is coupled to a receptor on a membrane inside a cell (left), while an ion channel is open at right. The G protein exists as a heterotrimer of alpha, beta and gamma subunits. It is initially bound to a molecule of GDP (guanosine diphosphate). When the receptor is triggered (flash), the GDP molecule is replaced by GTP (guanosine triphosphate) and the alpha unit and the GTP molecule detach. The alpha subunit then binds with another inner membrane-bound protein (green), the primary effector. This complex then travels to the ion channel (right) and causes it to close, releasing molecules of cGMP (cyclic guanosine monophosphate).
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