title: Spontaneous chiral symmetry breaking in early molecular networks.
abstract: BACKGROUND
  An important facet of early biological evolution is the selection of chiral enantiomers for molecules such as amino acids and sugars. The origin of this symmetry breaking is a long-standing question in molecular evolution. Previous models addressing this question include particular kinetic properties such as autocatalysis or negative cross catalysis.
  
  
  RESULTS
  We propose here a more general kinetic formalism for early enantioselection, based on our previously described Graded Autocatalysis Replication Domain (GARD) model for prebiotic evolution in molecular assemblies. This model is adapted here to the case of chiral molecules by applying symmetry constraints to mutual molecular recognition within the assembly. The ensuing dynamics shows spontaneous chiral symmetry breaking, with transitions towards stationary compositional states (composomes) enriched with one of the two enantiomers for some of the constituent molecule types. Furthermore, one or the other of the two antipodal compositional states of the assembly also shows time-dependent selection.
  
  
  CONCLUSIONS
  It follows that chiral selection may be an emergent consequence of early catalytic molecular networks rather than a prerequisite for the initiation of primeval life processes. Elaborations of this model could help explain the prevalent chiral homogeneity in present-day living cells.
authors.affiliation: Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Ran
authors.initials: R
authors.lastname: Kafri
authors.forename: Omer
authors.initials: O
authors.lastname: Markovitch
authors.forename: Doron
authors.initials: D
authors.lastname: Lancet
mesh_terms: D019143:Evolution, Molecular; D008962:Models, Theoretical; D000069497:Origin of Life; D013237:Stereoisomerism