Opsin
Opsin
Opsin (pronounced /ˈɒpsɪn/) is a protein that, together with the pigment retinal, constitutes the photopigments, which are light-sensitive molecules found in the photoreceptor cells of the retina.
Etymology
The term "opsin" originates from the Greek word "opsis," meaning "view" or "sight."
Function
Opsins are integral membrane proteins that span the disc membrane of the outer segment of photoreceptor cells. They are coupled to a G protein that triggers a cascade of biochemical activities that lead to a change in the cell's membrane potential. This change in potential is the first step in the conversion of light into a neural signal in the process of vision.
Types of Opsin
There are several types of opsin, each sensitive to different wavelengths of light. These include:
- Rhodopsin: Found in rod cells, which are responsible for vision in low light conditions.
- Photopsin: Found in cone cells, which are responsible for color vision.
- Melanopsin: Found in intrinsically photosensitive retinal ganglion cells, which are involved in the regulation of circadian rhythms and pupillary reflex.
Related Terms
- Photoreceptor Cell: A type of neuron in the retina that converts light into signals that can be processed by the brain.
- Retinal: A form of vitamin A that functions as a photoreceptor in the retina.
- G Protein: A family of proteins involved in transmitting signals from a variety of stimuli outside a cell to its interior.
External links
- Medical encyclopedia article on Opsin
- Wikipedia's article - Opsin
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