Rodopsiinipigmentti

Rodopsiinipigmentti, also known as visual purple, is a light-sensitive pigment found in the rod cells of the retina. It plays a crucial role in vision, particularly in low-light conditions. Rodopsiinipigmentti is a G protein-coupled receptor that consists of a protein molecule called opsin and a covalently bound chromophore, 11-cis-retinal, which is a derivative of vitamin A.

When light strikes the retina, it is absorbed by the rodopsiinipigmentti. This absorption causes a conformational change in the molecule, converting 11-cis-retinal to all-trans-retinal. This change triggers a cascade of biochemical reactions within the rod cell, ultimately leading to the generation of an electrical signal that is transmitted to the brain via the optic nerve. This signal is interpreted by the brain as a visual image.

In bright light, rodopsiinipigmentti becomes bleached, meaning the all-trans-retinal detaches from the opsin. This makes the rod cells temporarily less sensitive to light. The pigment must then be regenerated in a process that requires vitamin A to convert all-trans-retinal back to 11-cis-retinal. This regeneration process is slower than the bleaching process, which is why vision takes time to adapt when moving from bright light to darkness. A deficiency in vitamin A can lead to impaired night vision, a condition known as nyctalopia. Rodopsiinipigmentti is essential for scotopic vision, the type of vision that allows us to see in dim light.