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Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells (rods and cones) in the vertebrate retina.A photon is absorbed by a retinal chromophore (each bound to an opsin), which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve.
The visual cycle is a process in the retina that replenishes the molecule retinal for its use in vision.Retinal is the chromophore of most visual opsins, meaning it captures the photons to begin the phototransduction cascade.
The steps that apply to the phototransduction pathway from vertebrate rod/cone photoreceptors are: The Vertebrate visual opsin in the disc membrane of the outer segment absorbs a photon, changing the configuration of a retinal Schiff base cofactor inside the protein from the cis-form to the trans-form, causing the retinal to change shape.
Light signal transduction involves an enzyme cascade of G-proteins , cGMP phosphodiesterase, closure of a cation channel and ultimately hyperpolarization of the visual photoreceptor cell. [ 13 ] The visual rhodopsins of arthropods and molluscs differ from the vertebrate proteins in their signal transduction cascade involving G-proteins ...
The visual cycle is a circular enzymatic pathway, which is the front-end of phototransduction. It regenerates 11-cis-retinal. For example, the visual cycle of mammalian rod cells is as follows: all-trans-retinyl ester + H 2 O → 11-cis-retinol + fatty acid; RPE65 isomerohydrolases; [30]
It is only activated when 11-cis-retinal absorbs a photon of light and isomerizes to all-trans-retinal, [37] [38] the receptor activating form, [39] [40] causing conformal changes in rhodopsin (bleaching), [39] which activate a phototransduction cascade. [41] Thus, a chemoreceptor is converted to a light or photo(n)receptor. [16]
PDE6 is a protein complex located on the photoreceptor's outer segment, and plays an important role in the phototransduction cascade. [10] There are two types of photoreceptors: cones and rods . The rod and cone PDE6 complexes have different structures.
When the retina of the eye detects light, a reaction known as a phototransduction cascade occurs. It is a signal transduction pathway that leads to the activation of the enzyme phosphodiesterase, which hydrolyzes cGMP into 5’-GMP, decreasing the concentration of cGMP. In the absence of cGMP, the CNG channels in the photoreceptors close ...