Normalised absorption spectra of the three human photopsins and of human rhodopsin (dashed).

Photopsins are the photoreceptor pigments found in the cone cells of the retina that are the basis of color vision. Photopsins are very close analogs of the visual purple rhodopsin that is used in night vision. Photopsins consist of a protein called opsin and a bound chromophore, the retinal. Different opsins differ in a few amino acids and absorb light at different wavelengths as retinal-bound pigments. Opsins are G protein-coupled receptors. Isomerization of 11-cis-retinal into 11-trans-retinal by light induces a conformational change in the protein that activates the associated G protein and triggers a second messenger cascade. Spectral absorption curves of the short (S), medium (M) and long (L) wavelength pigments in human cone and rod (R) cells. ... Spectral absorption curves of the short (S), medium (M) and long (L) wavelength pigments in human cone and rod (R) cells. ... A photoreceptor is a specialized form of cell (specifically, neuron) that is capable of phototransduction. ... For animal and plant pigments, see Pigment, biology. ... Normalised absorption spectra of human cone (S,M,L) and rod (R) cells Cone cells, or cones, are cells in the retina of the eye which only function in relatively bright light. ... Human eye cross-sectional view. ... Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect or emit. ... A rhodopsin molecule (yellow) with bound retinal (orange), embedded in a cell membrane (lipids shown as green, head groups as red/blue). ... Night-vision is seeing in the dark. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... A chromophore is part (or moiety) of a molecule responsible for its color. ... In the vision system, retinal, technically called retinene1 or retinaldehyde, is a light-sensitive retinene molecule found in the photoreceptor cells of the retina. ... The general structure of an amino acid molecule, with the amine group on the left and the carboxyl group on the right. ... The wavelength is the distance between repeating units of a wave pattern. ... Figure 1. ... In chemistry, isomerization is the transformation of a molecule into a different isomer. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength [citation needed]. The elementary particle that defines light is the photon. ... G-proteins, short for guanine nucleotide binding proteins, are a family of proteins involved in second messenger cascades. ... In biology, second messengers are low-weight diffusible molecules that are used in signal transduction to relay signals within a cell. ...

In humans there are three different iodopsins (rhodopsin analogs) that form the pigments photopsin I, II, and III. They are called erythrolabe, chlorolabe, and cyanolabe, respectively . These photopsins have absorption maxima for yellowish-green (photopsin I), green (photopsin II), and bluish-violet light (photopsin III). George Wald got the 1967 Nobel Prize in Physiology or Medicine for his experiments in the 1950s that showed the difference in absorbance by these photopsins (see image). Human beings are defined variously in biological, spiritual, and cultural terms, or in combinations thereof. ... George Wald (November 18, 1906–April 12, 1997) was an American scientist who is best known for his work with pigments in the retina. ... 1967 (MCMLXVII) was a common year starting on Sunday of the Gregorian calendar (the link is to a full 1967 calendar). ... List of Nobel Prize laureates in Physiology or Medicine from 1901 to the present day. ... The 1950s was the decade spanning the years 1950 to 1959. ...

See also

• Rhodopsins, the pigment for monochromatic (scotopic) dark vision.
• Melanopsin, the pigment which is used to control pupil sizes and the sleep/wake cycle

A rhodopsin molecule (yellow) with bound retinal (orange), embedded in a cell membrane (lipids shown as green, head groups as red/blue). ... Melanopsin is a photopigment found in specialized ganglion cells of the retina that are involved in the regulation of circadian rhythms and pupillary reflex. ...

External links

• Rhodopsin and the eye, an excellent summary with pictures.

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