Phototransduction uses a signal transduction cascade similar to mechanisms stimu
ID: 68887 • Letter: P
Question
Phototransduction uses a signal transduction cascade similar to mechanisms stimulated by hormones and neurotransmitters. However, the visual sensory apparatus is stimulated by photons, and converts light energy into a nerve impulse. Determine whether each of the the following events increases phototransduction or does not increase phototransduction (either by not initiating a signal or by terminating the signal). The abbreviation cGMP is used for guanosine 3',5'-cyclic monophosphate (cyclic GMP), and PDE is used for phosphodiesterase.
Explanation / Answer
Ans: Determination of the Phototransduction cascade mechanisms wherein the event indicate that the Phototransduction serves as a model system for the dissection of G-proteincoupled signaling cascades because this cascade displays exquisite sensitivity and specificity.In vertehrate photoreceptor neurons the light receptor
molecule rhodopsin is composed of a protein,opsin, covalently linked to a chromuphore, 1 l-cis retinal.Upon absorption of a photon of light, the chromophore is isomerized from the I l-cis to the all-tram This change in the conformation of the chromophore leads to a change in the conformation of the protein and to the activation of its catalytic properties. Activated rhodopsin, or metarhodopsin, activates the heterotrimeric G protein transducin, which in turn leads to the activation of a phosphodiesterase (PDE). PDE hydrolyses cGMP to GME causing a transient decrease in cellular cGMP levels. The reduction in cGMP re,- suits in the closure of cGMP-gated cationic channels in the plasma membrane and a decrease in calcium influx.In the vertebrate visual cascade, the light-induced calcium decrease has been shown to modulate multiple signalling components. Receptor lifetime, second-messenger lifetime and channel activity are regulated by calcium changes.