Origins of biomolecular handedness

Abstract

Classical mechanisms proposed for the transition from racemic geochemistry to homochiral biochemistry in terrestrial evolution generally ascribe to chance the particular handed choice of the L-amino acids and the D-sugars by self-replicating systems. The parity-violating weak neutral current interaction gives rise to an energy difference between a chiral molecule and its mirror-image isomer, resulting in a small stabilization of the L-amino acids and the L-peptides in the alpha-helix and the beta-sheet conformation relative to the corresponding enantiomer. The energy difference suffices to break the chiral symmetry of autocatalytic racemic reaction sequences in an open non-equilibrium system.

Nonclassical forces: Seemingly insignificant but a powerful tool to control macromolecular structures

“…Theoretical studies revealed that very small, parityviolating weak neutral currents at the molecular level may distinguish mirror-imaged molecules and thus, be a basis for several amplification and detection mechanisms. [72][73][74][75][76] Recent literature cites claims of insignificantly small but still questionable differences seen between chiral isomers in their condensed states, like in supersaturated solutions, in crystals, in micellar aggregates, and on solid surfaces, etc. [77][78][79] Such a finding can have far-reaching implications, since, according to their propositions, these asymmetrical weak nuclear forces propagate to millions of other molecules via weak noncovalent interactions and land-up building asymmetrical population preferring a particular handedness.…”

Determining Amino Acid Chirality in the Supernova Neutrino Processing Model

“…The favored mechanism by which amplification could occur, autocatalysis, was originally suggested by Frank [10], but has been elaborated since by others [11][12][13]. More significantly, it has been demonstrated experimentally [44][45][46][47], thus showing that autocatalysis does actually work.…”

“…This is comparable to or greater than that achieved in other models, although direct comparison is difficult. As with any model of chirality selection, amplification, presumably by autocatalysis [10][11][12][13], which has been demonstrated to occur in laboratory experiments [44][45][46][47], is required to produce the order-of-a-few percent magnitudes of the enantiomeric excess observed in the meteorites, and the homochirality observed on Earth. Additional details of the SNAAP model are discussed in [14] and [19].…”

Determining Amino Acid Chirality in the Supernova Neutrino Processing Model

“…What is not well understood, however, is the mechanism by which the initial imbalance is produced, and the means by which it always produces the left-handed chirality observed in the amino acids. This enigma has been discussed in numerous reviews in past years (see, e.g., [8][9][10][11][12][13][14]). …”