Phototransduction. sapling learning Phototransduction uses a signal transduction
ID: 71810 • Letter: P
Question
Phototransduction.
sapling learning 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. Phototransduction increases Phototransduction does not increase PDE bound to inhibitory subunit [Cadeclines convers?GTPto cGMP 11-cis-retinal converted to all-trans-retinal Ta subunit encounters PDE [cGMP] decreases high [Ca2+] inhibits guanylyl cyclase GDP bound to transducin Ta subunit hydrolyzes GTP cGMP PDE converts cGMP transducin dissociates into Tr GTP and Toy to biologically inactive 5'-GMP cGMP-gated ion channels closeExplanation / Answer
SOLUTION:
Photo transduction increases or decreases:
Phosphodiesterase or PDE.
GTPase Accelerating Protein (GAP) interacts with the alpha subunit of transducin, and causes it to hydrolyse its bound GTP to GDP, and thus halts the action of phosphodiesterase, stopping the transformation of cGMP to GMP.
Guanylate Cyclase Activating Protein (GCAP) is a calcium binding protein, and as the calcium levels in the cell have decreased, GCAP dissociates from its bound calcium ions, and interacts with Guanylate Cyclase, activating it. Guanylate Cyclase then proceeds to transform GTP to cGMP, replenishing the cell's cGMP levels and thus reopening the sodium channels that were closed during phototransduction.
Finally, Metarhodopsin II is deactivated. Recoverin, another calcium binding protein, is normally bound to Rhodopsin Kinase when calcium is present.
When the calcium levels fall during phototransduction, the calcium dissociates from recoverin, and rhodopsin kinase is released, when it proceeds to phosphorylate metarhodopsin II, which decreases its affinity for transducin.
Finally, arrestin, another protein, binds the phosphorylated metarhodopsin II, completely deactivating it.
So thus thephototransduction is deactivated, and the dark current and glutamate release is restored. It is this pathway, where Metarhodopsin II is phosphorylated and bound to arrestin and thus deactivated
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