The Chemistry of Vision

A photon, a particle of light emitted into space by the sun at the speed of light, reaches the earth in four and a half minutes at the most. Here, with many of its fellows, it may hit the petal of a wild yellow chrysanthemum. Most photons landing on the flower are absorbed into it. Only a few, which reach the petal at the right wavelength, are reflected from it and reach our eyes, where they collide with retinal proteins. This is the first stage in the enigmatic process of vision.

Our photon was emitted by the sun, reached the earth, and bounced off the petal directly into the retinal proteins in our eyes. There, within less then a tenth of a millionth of a millionth of a second, it roused a retinal molecule, changing the protein’s structure. This determined the kind of signal it would dispatch to
the brain.

The change in the retinal protein’s structure, which begins from the instant of impact with the photon, depends on its link with a small molecule that lurks within its coils, a derivative of vitamin A called “retinal.” It was long believed that the rotation of this retinal molecule was the first stage in vision. However, Prof. Mordechai Sheves of the Weizmann Institute’s Organic Chemistry Department revealed that the retinal protein’s structure changes even when rotation of its internal retinal molecule is prevented, suggesting that the visual process starts even earlier. Research on vision’s first instants could help us understand blindness and color blindness. In addition, it could lead to a broadening of the color spectrum seen by the
human eye.