Sandbox Reserved 1451: Difference between revisions

Rhodopsin performs two functions. One function is to bind retinal.  Rhodopsin is a protein that is essential for vision, especially in dim light. The photoreceptors in the retina that contain rhodopsin are rods. Rhodopsin is attached to 11-cis retinal which becomes excited by a photon of light and isomerizes to become all-trans conformation (NOTABILITY). This excitation activates rhodopsin and leads to depolarizing of neurons. The depolarizing of neurons is how the image is transmitted to the brain<ref name="Article1">https://ghr.nlm.nih.gov/gene/RHO#</ref>.  (https://ghr.nlm.nih.gov/gene/RHO#) Another function is to function as a G protein-coupled receptor. When rhodopsin is activated by light the protein couples with the G protein transducin which is the first step in the signal cascade (PDF ON NOTABILITY) Rhodopsin must undergo several conformational changes before being able to bind transducin. (ALTERATIONS) Rhodopsin is initially converted to metarhodopsin II which is the active form of rhodopsin. Once the protein is active then metarhodopsin binds the G-protein tranducin and the GDP is exchanged for GTP. The G protein subunits dissociate and causes a decrease in cytosolic cGMP. The decrease in cGMP also causes the closing of calcium channels. When calcium concentrations drop the photoreceptors become hyperpolarized and this ensures the action potential is sent onward toward the brain. (RHODOPSIN AND RP). Photoreceptors are unable to be immediately restimulated, rhodopsin kinase phosphorylates the protein on serine and threonine residues which leads to the binding of arrestin. Arrestin prevents rhodopsin from interacting with tranducin again, thus preventing restimulation of the protein. Arrestin is released from the protein via phospotase A which dephosphorylates rhodopsin. (RHODOPSIN AND RP)