Homochirality

Homochirality refers to uniform handedness among chiral molecules in a system. In biology on Earth, life uses proteins made from L-amino acids and nucleic acids with D-sugars.

Chirality matters because enantiomers have identical physical properties in achiral environments; however, biological interactions are highly stereospecific, so a molecule's handedness strongly influences binding, catalysis, and structure. Homochirality aids consistent folding, catalytic efficiency, and polymerization; even slight mixtures can hinder enzyme activity and proper assembly.

Origins: Several hypotheses; parity violation would produce minuscule energy differences; circularly polarized light from astrophysical sources could bias production; autocatalytic models show that a small initial excess can be amplified to near-complete homochirality; the Soai reaction demonstrates enantioenrichment in the lab; no consensus on prebiotic plausibility.

In biology, the uniformity of handedness is exemplified by proteins built from L-amino acids and nucleic acids employing D-sugars, a combination that underpins precise three-dimensional structure and function. Research into how homochirality arose continues to explore chemical, physical, and evolutionary mechanisms, as well as its implications for the origin of life and the design of chiral drugs and catalysts.