visual purple

purple /pur·ple/ (pur´p'l)

1. a color between blue and red.

2. a substance of this color used as a dye or indicator.

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visual purple  rhodopsin.

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visual purple

n.

See rhodopsin.

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visual purple.

See rhodopsin.

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purple

1. a color between blue and red.

2. a substance of this color used as a dye or indicator.

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purple cudweed

gnaphalium purpureum.

purple-flowered bell vine

ipomoeapurpurea.

purple-flowered morning glory

ipomoeapurpurea.

purple-leafed goosefoot

scleroblitum atriplicinum.

purple loco

astragalusmollisimus.

purple mint

perilla frutescens.

purple pigeon grass

setariaincrassata.

purple plume grass

triraphis mollis.

purple rattlebox

sesbaniapunicea.

purple top

verbenabonariensis.

purple sesbane

sesbaniapunicea.

purple viper's bugloss

echiumplantagineum.

visual purple

rhodopsin.

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rhodopsin 

Visual pigment contained in the outer segments of the rod cells of the retina and involved in scotopic vision. When light stimulates the retina, the chromophore of the pigment molecule '11-cis' retinal (which is vitamin A aldehyde) isomerizes to 'all-trans' retinal. This leads to other chemical transformations which carry on even in the absence of light. The first stage is prelumirhodopsin, then lumirhodopsin and finally metarhodopsin (of which there are two types). This last transformation may lead to the breakdown of the molecule into retinal and opsin. The molecule is regenerated by recombining retinal and opsin with some enzymes. The absorption spectrum of rhodopsin has a maximum around 498 nm. The isomerization from '11-cis' to 'all-trans' also gives rise to the process of transduction in which the membrane potential covering the pigment molecules in the outer segment changes towards a hyperpolarization of the cell. This is the first step in the nervous response to a light stimulation of the retina. Syn. visual purple (not used any more); erythropsin. See dark adaptation; bleaching; receptor potential; absorption spectrum; transduction.