Abstract
Replicators are fundamental to the origin of life and evolvability. Biology exhibits homochirality: only one of two enantiomers is used in proteins and nucleic acids. Thermodynamic studies of chemical replicators able to lead to homochirality shed valuable light on the origin of homochirality and life in conformity with the underlying mechanisms and constraints. In line with this framework, enantioselective hypercyclic replicators may lead to spontaneous mirror symmetry breaking (SMSB) without the need for additional heterochiral inhibition reactions, which can be an obstacle for the emergence of evolutionary selection properties. We analyze the entropy production of a two-replicator system subject to homochiral cross-catalysis which can undergo SMSB in an open-flow reactor. The entropy exchange with the environment is provided by the input and output matter flows, and is essential for balancing the entropy production at the non-equilibrium stationary states. The partial entropy contributions, associated with the individual elementary flux modes, as defined by stoichiometric network analysis (SNA), describe how the system’s internal currents evolve, maintaining the balance between entropy production and exchange, while minimizing the entropy production after the symmetry breaking transition. We validate the General Evolution Criterion, stating that the change in the chemical affinities proceeds in a way as to lower the value of the entropy production.
Highlights
The importance of studying chemical systems subject to various architectures, and capable of spontaneous mirror symmetry breaking (SMSB), owes to the problem of the origin of biological homochirality, an outstanding problem in origin of life research [1,2], as well as a crucial factor to take into account in the design of synthetic systems mimicking primordial processes of life
The current consensus is that the homochirality of biological compounds: the observed bias in biopolymers made up from homochiral L-amino acids and D-sugars is a condition associated with life that most likely emerged through processes of spontaneous mirror symmetry breaking very early on during abiotic chemical evolution [2]
Enantioselective hypercycles enable quadratic autocatalysis to achieve the enantioselective behavior of cubic autocatalysis, and may lead to spontaneous mirror symmetry breaking for specific reaction rate constants in systems with thermodynamic architectures that maintain them out of equilibrium with their surroundings [17]
Summary
The importance of studying chemical systems subject to various architectures, and capable of spontaneous mirror symmetry breaking (SMSB), owes to the problem of the origin of biological homochirality, an outstanding problem in origin of life research [1,2], as well as a crucial factor to take into account in the design of synthetic systems mimicking primordial processes of life. Enantioselective hypercycles enable quadratic (first order) autocatalysis to achieve the enantioselective behavior of cubic (second-order) autocatalysis, and may lead to spontaneous mirror symmetry breaking ( resulting in a chiral final stationary state instead of a racemic one) for specific reaction rate constants in systems with thermodynamic architectures that maintain them out of equilibrium with their surroundings [17] The significance of such a SMSB reaction network is that it does not imply heterochiral inhibiting reactions, such as those of the Frank-like models, and as a consequence, the emergence of biological homochirality could already be included, both theoretically and experimentally, in the current models of the selection and evolution of biological replicators. This will lead to a description of entropy production, entropy exchange, and the balance of the former and the latter at a NESS, for non-equilibrium systems in terms of the extreme flux modes, as defined by stoichiometric network analysis (SNA) [18]
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