Rhodopsin
Rhodopsin (also known as visual purple) is a type of photoreceptor cell in the eye that is responsible for the detection of light. It is a biological pigment found in the rods of the retina and is a G-protein-coupled receptor (GPCR).
Rhodopsin is extremely sensitive to light, and thus enables vision in low-light conditions. When exposed to light, the pigment immediately photobleaches, and it takes about 30 minutes to regenerate fully in humans.
Structure[edit | edit source]
Rhodopsin is composed of a protein moiety called opsin and a covalently bound cofactor called retinal, a photoreactive chromophore. Opsin is a seven-transmembrane domain protein, and its structure is primarily determined by its seven alpha helices.
Function[edit | edit source]
The primary function of rhodopsin is to detect light, which it does through a process called phototransduction. This process involves a series of steps:
- Absorption of a photon by the retinal component of rhodopsin.
- Isomerization of 11-cis-retinal to all-trans-retinal.
- Activation of the G protein transducin by the opsin component of rhodopsin.
- Activation of phosphodiesterase, which hydrolyzes cyclic GMP.
- Closure of cyclic GMP-gated ion channels in the plasma membrane, leading to hyperpolarization of the cell and transmission of the signal to the brain.
Clinical significance[edit | edit source]
Mutations in the gene encoding rhodopsin can lead to various forms of retinitis pigmentosa, a group of hereditary diseases that result in progressive vision loss. These mutations can affect the stability of the rhodopsin molecule, its ability to bind to 11-cis-retinal, or its ability to activate transducin.
See also[edit | edit source]
References[edit | edit source]
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