Biology – Quantitative Biology – Biomolecules
Scientific paper
Jul 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996aipc..379...17b&link_type=abstract
Physical orgin of homochirality in life. AIP Conference Proceedings, Volume 379, pp. 17-49 (1996).
Biology
Quantitative Biology
Biomolecules
8
Structure And Bonding, Conformation
Scientific paper
The indispensable role played by homochirality and chiral homogeneity in the self-replication of crucial biomolecules is stressed, with the conclusion that life could neither exist nor originate without these chiral molecular attributes. Hypotheses historically proposed for the origin of chiral molecules on Earth are reviewed, including biogenic theories as well as abiotic theories embracing both indeterminate and determinate mechanisms. Indeterminate mechanisms, including autocatalytic symmetry breaking, asymmetric adsorption on quartz and clay minerals, and asymmetric syntheses in chiral crystals, are discussed and evaluated in the context of the prebiotic environment. Abiotic determinate mechanisms based on electric, magnetic and gravitational fields, on circularly polarized light (CPL), and on parity violation effects are summarized, with the emphasis that only CPL has proved practicable experimentally, but that it would be implausible on the primitive Earth. Mechanisms for the amplification of small, indigenous enantiomeric excesses are discussed, with one involving the partial polymerization of amino acids and the partial hydrolysis of polypeptides suggested as potentially viable prebiotically. Aspects of the turbulent, chirality-destructive primeval environment are described, with the conclusion that all of the above mechanisms for the terrestrial prebiotic origin of chirality would be non-viable, and that an alternative extraterrestrial source for the accumulation of chiral molecules on primitive Earth must have been operative. A scenario for this is outlined, in which we postulate that asymmetric photolysis of the organic mantles on interstellar grains in molecular clouds by circularly polarized ultraviolet synchrotron radiation from the neutron star remnants of supernovae produces chiral molecules in the grain mantles. These grains with their chiral mantles are ultimately accumulated by Earth as the planet sweeps through the molecular clouds, or by impact delivery to Earth during the prebiotic era after incorporation of the grains into comets or asteroids.
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