Abstract
Chiral symmetry breaking in far from equilibrium systems with large number of amino acids and peptides, like a prebiotic Earth, was considered. It was shown that if organic catalysts were abundant, then effective averaging of enantioselectivity would prohibit any symmetry breaking in such systems. It was further argued that non-linear (catalytic) reactions must be very scarce (called the abundance parameter) and catalysts should work on small groups of similar reactions (called the similarity parameter) in order to chiral symmetry breaking have a chance to occur. Models with 20 amino acids and peptide lengths up to three were considered. It was shown that there are preferred ranges of abundance and similarity parameters where the symmetry breaking can occur in the models with catalytic synthesis / catalytic destruction / both catalytic synthesis and catalytic destruction. It was further shown that models with catalytic synthesis and catalytic destruction statistically result in a substantially higher percentage of the models where the symmetry breaking can occur in comparison to the models with just catalytic synthesis or catalytic destruction. It was also shown that when chiral symmetry breaking occurs, then concentrations of some amino acids, which collectively have some mutually beneficial properties, go up, whereas the concentrations of the ones, which don’t have such properties, go down. An open source code of the whole system was provided to ensure that the results can be checked, repeated, and extended further if needed.
Highlights
The problem of chiral symmetry breaking in live matter or why life forms use only L enantiomers of amino acids and D enantiomers of sugars has been the subject of great scientific interest and extensive research since the discovery of enantiomers by Louis Pasteur more than 150 year ago
It was further shown that models with catalytic synthesis and catalytic destruction statistically result in a substantially higher percentage of the models where the symmetry breaking can occur in comparison to the models with just catalytic synthesis or catalytic destruction
It was argued that the number of different organic molecules, including organic catalysts must have been very large on prebiotic Earth
Summary
The problem of chiral symmetry breaking in live matter or why life forms use only L enantiomers of amino acids and D enantiomers of sugars has been the subject of great scientific interest and extensive research since the discovery of enantiomers by Louis Pasteur more than 150 year ago. As discussed in the introduction, such reactions (for example catalytic synthesis of amino acids) were considered in many works related to chiral symmetry breaking:. Given that we used 20 amino acids (40 when accounted for left and right ones), there are 129,600 distinct reactions responsible for formation of peptide chains (half of that if we count only unique ones and impose a global symmetry to get matching enantiomeric reaction) and there are potentially 2,560,000 catalytic synthesis reactions to choose from, of which the distributions “choose” somewhere between 200 to 2000 depending on the parameters. Since the symmetry multiplier is 4 (there are 4 reactions for each chosen pair), that means that the average number of catalytic reactions was about 26 in a given model with this value of abundance parameter and before similarity parameter was applied. This is just a single reaction, so no distribution was needed
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