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MECHANISM |
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(1)11-cis retinal and opsin in a rod cell combine to form Rhodopsin.(2/3) Chemical changes occur following the absorption of a photon of light.(4) After transduction occurs metarhodopsin II dissociates into all-trans retinal which isomerises as the cycle begins again.(5) The key step in the mechanism is step 3 the transduction of photon reception to a neural action potential.
ROLE OF ACTIVATED RHODOPSIN
The activated rhodopsin activates transducin which is a G protein so that it binds GTP. The transducin GTP complex then activates a specific phosphodiesterase which cleaves cGMP. This cleavage of cGMP stimulates an intracellular reaction that generates a visual signal to the brain.
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