The homochirality of biological molecules (right-handed sugars and left-handed amino acids) is a signature of life. Extensive research has been devoted to understanding how enrichment of one enantiomer over the other might have emerged from a prebiotic world. Here, we use experimental data from the model Soai autocatalytic reaction system to evaluate the energy required for symmetry breaking and chiral amplification in molecular self-replication. One postulate for the source of the original imbalance is the tiny difference in energy between enantiomers due to parity violation in the weak force. We discuss the plausibility of parity violation energy difference coupled with asymmetric autocatalysis as a rationalization for absolute asymmetric synthesis and the origin of the homochirality of biological molecules. Our results allow us to identify the magnitude of the energy imbalance that gives rise to directed symmetry breaking and asymmetric amplification in this autocatalytic system.
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All relevant data supporting the findings of this study are available within the paper and its Supplementary Information files and/or are available on request from the authors.
The Mathematica code used in this stochastic modelling is available on request from the authors.
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D.G.B. acknowledges funding from the Simons Foundation through the Simons Collaboration on the Origins of Life (SCOL 287625). N.A.H. acknowledges a US Department of Defense SMART (Science, Mathematics, and Research for Transformation) Scholarship for Service. We are grateful to D. K. Kondepudi for stimulating discussions and guidance in stochastic modelling. We also acknowledge helpful discussions with J. M. Brown, G. F. Joyce and S. E. Denmark.
The authors declare no competing interests.
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Supplementary information providing details of the experimental and computational methods, full tables of all experimental symmetry-breaking experiments, and figures showing the results of kinetic modelling.
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Hawbaker, N.A., Blackmond, D.G. Energy threshold for chiral symmetry breaking in molecular self-replication. Nat. Chem. 11, 957–962 (2019). https://doi.org/10.1038/s41557-019-0321-y
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