On the definition of a self-sustaining chemical reaction system and its role in heredity
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RESEARCH
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On the definition of a self-sustaining chemical reaction system and its role in heredity Yu Liu Abstract Background: The ability to self-sustain is one of the essential properties of life. However, a consistent and satisfying definition of self-sustainability is still missing. Currently, self-sustainability refers to either “no-intervention by a higher entity” or “regeneration of all the system’s components”. How to connect self-sustainability with heredity, another essential of life, is another problem, as they are often considered to be independent of each other. Last but not least, current definitions of self-sustainability failed to provide a practical method to empirically discern whether a chemical system is self-sustaining or not. Results: Here I propose a definition of self-sustainability. It takes into account the chemical reaction network itself and the external environment which is simplified as a continuous-flow stirred tank reactor. One distinct property of self-sustaining systems is that the system can only proceed if molecular triggers (or called, seeds) are present initially. The molecular triggers are able to establish the whole system, indicating that they carry the preliminary heredity of the system. Consequently, life and a large group of fires (and other dissipative systems) can be distinguished. Besides, the general properties and various real-life examples of self-sustaining systems discussed here together indicate that self-sustaining systems are not uncommon. Conclusions: The definition I proposed here naturally connects self-sustainability with heredity. As this definition involves the continuous-flow stirred tank reactor, it gives a simple way to empirically test whether a system is self-sustaining or not. Moreover, the general properties and various real-life examples of self-sustaining systems discussed here provide practical guidance on how to construct and detect such systems in real biology and chemistry. Reviewers: This article was reviewed by Wentao Ma and David Baum. Keywords: Definition of life, Origin of life, Autocatalysis, Self-replication, Non-equilibrium, CSTR, Molecular trigger, Molecular seed, Limited heredity Background NASA defines life as a self-sustaining chemical system capable of undergoing Darwinian evolution [1, 2]. Here, “self-sustaining” implies that a living system should not need continuous intervention by a higher entity (e.g. a graduate student or a god) to continue as life [1]. Another popular definition of life comes from the concept of autopoiesis: a system is said to be living if it is capable of Correspondence: [email protected] Institut Mittag-Leffler, Auravägen 17, 18260 Djursholm, Sweden
self-sustaining owing to an inner network of reactions that regenerate all the system’s components [3]. But the phrase “self-sustaining” refers to “no-intervention” in the former definition, but “regeneration” in the latter. In the fields that relate to essentials of life, such as biochemistry [4, 5], molecular biology [6], network auto
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