Chirality

But chirality, or handedness, is an essential characteristic of the molecules of life. Most naturally occurring organic molecules are chiral, meaning that they are distinct from their mirror images in the same way that our right and left hands differ.

In the lab, chemical reactions that synthesize amino acids and sugars create the right- and left-handed versions of the molecules in equal amounts. Life on Earth, however, uses one version almost exclusively, preferring what are conventionally called right-handed sugars and left-handed amino acids.

- Science News (read full article here)