| Visual Cycle |
Article Index for Visual |
Website Links For Visual |
Information AboutVisual Cycle |
| CATEGORIES ABOUT VISUAL CYCLE | |
| vision | |
| sensory receptors | |
| pigments | |
| color | |
| metabolism | |
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The visual cycle is the biological conversion of a Photon into an Action Potential in the Retina . This process occurs via G-protein Coupled Receptor s called Opsin s which contain the Chromophore 11-cis Retinal . 11-cis Retinal is covalently linked to the Opsin receptor via a Schiff Base forming a Retinylidene Protein . When struck by a Photon , 11-cis Retinal undergoes Photoisomerization to All-trans Retinal which changes the conformation of the Opsin GPCR leading to Signal Transduction cascades which ultimately causes an Action Potential resulting in Visual Perception . Following isomerization and release from the Opsin protein, All-trans Retinal is reduced to all-trans Retinol and travels back to the Retinal Pigment Epithelium to be "recharged". It is first Esterified by Lecithin-retinol Acyltransferase (LRAT) and then converted to 11-cis Retinol by the isomerohydrolase RPE65 . Finally, it is oxidized to 11-cis Retinal before traveling back to the Rod outer segment where it can again be conjugated to an Opsin to form a new, functional visual pigment ( Rhodopsin ). REFERENCES
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