QS Study

Rhodopsin-Retinal visual cycle

Rhodopsin is very sensitive to light and is responsible for night vision. Rhodopsin and its decomposition by Light Energy, the outer section of the rod that projects into the pigment layer of the retina has a concentration of about 40 percent of the light-sensitive pigment called rhodopsin, or visual purple.

Fig: Processing of Vitamin A in the Visual Cycle

  • When light energy is absorbed by rhodopsin, the rhodopsin breaks down into opsin (scotopsin) and retinine (All-trans retinal) through a series of the intermediate compound.
  • Some of all-transretinal are reduced to all-transretinol (Vitamin-A).
  • In dark all-transretinal and all-transretinal (vitamin A) is converted into II-Cis retial or II-cis retinol by the enzyme isomerase.
  • II-cis retinal combined with scotopsin (opsin to form rhodopsin).
  • In rods, the visual cycle consists of bleaching and recycling of retinoids between the photoreceptors and the retinal pigment epithelium (RPE)

The retinal is a particular type called 11-cis-retinal. This is the form of retinal is important because only this form can bind with scotopsin to synthesize rhodopsin.