You might expect living cells to be composed of a random soup of materials — but look closely and you’ll find they’re built from molecules with distinct orientation preferences. How did life’s preferred “handedness” arise?
Billions of years ago, perhaps on the barely-solidified crust of young Earth, life somehow arose from non-living matter. Today, we still haven’t solved the puzzle of how this transition from non-living to living occurred — but nature has left behind some helpful clues, including the intriguing geometry of life’s building blocks.
This generic amino acid exists in both a left-handed and a right-handed form: all the same things are attached in the same order, but the two forms are mirror images and cannot be superimposed. If both forms exist, why is life built from only left-handed amino acids? [Public Domain]Many organic molecules come in two forms: left-handed and right-handed versions that are mirror images of each other. Just as you can’t put a left-handed glove onto your right hand, the mirror images of these chiral molecules are distinct and cannot be superimposed.
But while the pre-biological soup of material on early Earth contained both left-handed and right-handed forms of chiral molecules, living organisms ...