Retinal
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Retinal is a polyene chromophore. It binds to opsin proteins and forms the chemical basis of visual phototransduction, the light-detection stage of visual perception.
An opsin protein surrounds a molecule of 11-cis retinal, awaiting the arrival of a photon. Once the retinal molecule captures a photon, its configuration change causes it to push against the surrounding opsin protein which may cause the opsin to send a chemical signal to the brain indicating that light has been detected. Retinal is then converted back to its 11-cis configuration by ATP phosphorylation, and the cycle begins again.
Retinol
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Retinol is a hydrolytic metabolite of retinyl esters belonging to the group of vitamin A1 as an alcohol form. Retinol or other forms of vitamin A are fat-soluble vitamins that are found in food and us
Retinal
…other carotenoids can be converted by animals to retinal. Some carnivores cannot convert any carotenoids at all. The other main forms of vitamin A – retinol and a partially active form, retinoic acid – may both be produced from retinal. Invertebrates such as insects and squid use hydroxylated forms of retinal…
Frederick Gowland Hopkins, 1929 Nobel Prize for Physiology or Medicine
George Wald, 1967 Nobel Prize for Physiology or Medicine