This dynamic illustration (animation) of the Signal Transduction idea represents Martin Rodbell's revolutionary concept of how cells sense their environment. The small red spheres represent the extracellular signals such as hormones, growth factors, cytokines, odorants, taste molecules, ions, light, etc. The large green sphere represents the receptor that discriminates and binds extracellular signals. The yellow represents the transducer (G-protein), which not only affects the binding properties of the receptor to extracellular signals, but also is required for activation (or, in some cases, inhibition not represented here) of a target protein known as the effector (green) such as adenylyl cyclase. This concept is still unchallenged, despite of being more than three decades old. It represents a departure from the model proposed by Dr. Earl Sutherland, suggesting that the enzyme adenylyl cyclase was both a receptor and an effector for extracellular signals (wire framed green bullet, just before the appearance of the three spheres). The goal of the animation is to represent the dynamic aspect of the system that is critical to the signal transduction process. Although most authors consider the transduction process to be unidirectional--the receptor receives the signal, and then activates the transducer that, in turn, stimulates or inhibits an effector--Rodbell's view was more complex, since he thought that the receptor is influenced also by the transducer which, in turn, is affected by the activity of the effector as well (cycling white grains). Thus, this animation faithfully represents Rodbell's thinking and was made as a tribute to him. Description provided by Fernando Ribeiro-Neto, April 2000
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