A Magic of Cis - Trans Isomerization and Light Induced Molecular Changes |
When visible light hits the chromospheres (retinal), a p electron is promoted toa higher-energy orbital, allowing free rotation about the bond between carbonatom 11 and carbon atom 12 of the retinal molecule. About half the time, thisrotation leads to the isomerization of retinal when the p electron returns to thelower-energy orbital. When retinal isomerizes, a conformational change in theprotein opsin occurs. This conformational change initiates a cascade ofbiochemical reactions that result in the closing of Na+ channelsin the cell membrane. When the Na+ channels are closed, a largepotential difference builds up across the plasma membrane, and the potentialdifference is passed along to an adjoining nerve cell as an electrical impulse.The nerve cell carries this impulse to the brain, where the visual informationis interpreted.