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What is During the dark phase of visual cycle, which form of vitamin A combines with opsin to make Rhodopsin and explain in detail?
Rhodopsin is the photosensitive visual pigment present in the discs of the rod outer segments. It consists of a protein opsin and a carotenoid called retinal or retinene (aldehyde of vitamin A). The light absorbed by the rhodopsin conves its 11-cis-retinal into all-trans-retinal. This light-induced isomerization of 11-cis-retinal into all-trans-retinal occurs through formation of many intermediates which exist for a transient period. In the retina, under constant light stimulation, a steady state must exist under which the rate at which they are regenerated. This equilibrium between the photodecomposition and regeneration of visual pigments is referred to as visual cycle. Ref: guyton and hall textbook of medical physiology 12 edition page number: 742,743,744