Rhodopsin

Rhodopsin is the light-sensitive receptor pigment in vertebrate rod cells. Its absorption of a photon triggers a molecular cascade that enables vision in dim conditions.

Retinal: Retinal is a vitamin A-derived molecule that absorbs light and changes shape within visual pigments. Its light-driven shape change is the first molecular event in rhodopsin activation.
Opsin: Opsin is a light-insensitive protein that binds a retinal chromophore to form a visual pigment. Rhodopsin consists of the rod-cell opsin protein bound to retinal.
Franz Christian Boll: Franz Christian Boll was a German physiologist who identified the light-sensitive red pigment in the retina in 1876. His observation of the retinal pigment began the scientific study of rhodopsin.
Scotopic vision: Scotopic vision is vision under low-light conditions, mediated primarily by rod photoreceptors. Rhodopsin’s high sensitivity to light makes it central to scotopic vision.
Cone opsin: A cone opsin is a light-sensitive receptor protein in cone photoreceptors, tuned to a range of visible wavelengths. Cone opsins support color and bright-light vision, unlike rod rhodopsin’s dim-light specialization.
Metarhodopsin II: Metarhodopsin II is the activated form of rhodopsin that stimulates the G protein transducin. This short-lived state transmits rhodopsin’s photon-triggered signal to transducin.
G protein-coupled receptor: A G protein-coupled receptor is a membrane protein that transmits signals by activating intracellular G proteins. Rhodopsin is a light-activated member of this large receptor family.
Willy Kühne: Willy Kühne was a German physiologist who studied visual purple and named it rhodopsin. His experiments linked the pigment’s bleaching to light exposure and visual function.
Dark adaptation: Dark adaptation is the gradual increase in visual sensitivity after moving from bright light into darkness. Rhodopsin regeneration contributes to the recovery of rod sensitivity in darkness.
Photopsin: Photopsins are visual pigments in cone cells, each containing an opsin paired with retinal. Photopsins are the cone-cell counterparts to rhodopsin in rods.

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