Biological Homochirality
Source: Donna Blackmond, Cold Spring Harbor Perspectives in Biology 2, 2010; review Chemical Reviews 119, 2019 Institution: Scripps Research Institute
Finding
All life uses exclusively L-amino acids in proteins and D-sugars in nucleic acids. Abiotic chemistry produces racemic mixtures. Somewhere in life’s origin, one handedness was selected and the other excluded. Mechanisms for amplification include Soai autocatalysis, chiral crystal surfaces, and circularly polarized light. The initial bias may have been random, amplified by autocatalytic processes. The origin remains an open question.
Pattern Mapping
Alignment — Homochirality is a commitment carried forward through time. The initial choice and all subsequent action are consistent. Every protein uses L-amino acids because the first ones did. Alignment as temporal consistency.
Proportion — The system uses one chirality, not both. This is a necessary constraint: mixed chirality would make protein folding and enzymatic catalysis unreliable. Excluding a viable alternative because consistency demands commitment.
Connections
- Chirality (MYSTERY) — the same phenomenon from the EARTH perspective: origin unknown
- Symmetry Breaking — chirality IS molecular symmetry breaking (→ Meta-Pattern 08: Symmetry Breaking)
- Cambrian Explosion — both: constraint enables subsequent diversity
- Mineral Evolution — molecular chirality cascades to geological consequences
- DNA Error Correction — both maintain structural consistency through exclusion of alternatives
Status
Established biochemistry. Mechanisms of amplification are active research. See Blackmond (2010); Soai et al., Nature 378, 1995. Origin of initial bias remains open. The mapping to the five properties is this project’s structural interpretation.
The mapping to the five properties is this project’s structural interpretation.