Life is remarkably selective. Life relies on many molecules with so-called “handedness” – they are chemically identical but mirror images of each other. Most chemical reactions produce a 50:50 mix of the left-handed and right-handed forms of a chemical, but life only uses one of these. Because of the differences between left- and right-handed chemicals, most of organisms’ key enzymes actually do not function when exposed to chemicals with the wrong handedness.
This presents something of a challenge for research into the origin of life, as we are forced to explain how a world that may have begun with an even mix of left- and right-handed chemicals gave rise to organisms that used only one of them.
Today’s Nobel Prize in Chemistry goes to two people, Henri Kagan and Kenso Soai, who discovered that chemical reactions can be distorted, producing large excesses of one of two forms of a chemical.
Chirality and life
The technical term for molecular handedness is “chirality,” and scientists replace “left” and “right” with “dextro” (D) and “levo” (L). But the ideas are largely the same. Your hands all have the same components—fingers and thumbs—that are organized in the same way. However, when you point your thumb upward, the fingers curl in opposite directions, making one a mirror image of the other. Depending on the arrangement of chemical bonds, many molecules can form similar mirror image shapes, with all the same parts oriented slightly differently in space.
(For the geek readers, carbon atoms have four potential bonding sites that are evenly distributed across the surface of the atomsphere. If each of these sites is linked to a different chemical, swapping the chemicals located in two of them can potentially change the arrangement in 3D space.)
