Retinal
Videos
Retinal is a polyene chromophore. Retinal, bound to proteins called opsins, is the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
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.
Xanthophyll
Videos
Xanthophylls are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes. The name is from Greek: xanthos (ξανθός), meaning "yellow", and phyllon (φύλλον), meaning "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments.
The characteristic color of egg yolk results from the presence of a xanthophyll pigment typical in color of lutein or zeaxanthin of the xanthophylls, a division of the carotenoids group.
Thin layer chromatography is used to separate components of a plant extract, illustrating the experiment with plant pigments that gave chromatography its name. Plant xanthophylls form the bright yellow band next to the green.