Abstract
Any living organism can be considered as a component of a dissipative process coupling an irreversible consumption of energy to the growth, reproduction and evolution of living things. Close interactions between metabolism and reproduction are thus required, which means that metabolism has two main functions. The first one, which is the most easily perceptible, corresponds to the synthesis of the components of living beings that are not found in the environment (anabolism). The second one, which is usually associated with the former, is the dissipative process coupling the consumption of energy to self-organization and reproduction and introducing irreversibility in the process. Considering the origin of life, the formation of at least some of the building blocks constituting a living organism can be envisaged in a close to equilibrium situation under reducing conditions (for instance in hydrothermal vents). However, coupling irreversibly self-organization with the dissipation of an energy flux implies far from equilibrium conditions that are shown in this work to raise quantitative requirements on the height of kinetic barriers protecting metabolites from a spontaneous evolution into deactivated species through a quantitative relationship with the time scale of the progress of the overall process and the absolute temperature. The thermodynamic potential of physical sources of energy capable of feeding the emergence of this capacity can be inferred, which leads to the identification of photochemistry at the wavelength of visible light or processes capable of generating activated species by heating transiently a chemical environment above several thousand Kelvin as the only processes capable of fulfilling this requirement.
Highlights
The main features of the living state can be identified even though a comprehensive definition of what is life may be difficult to reach [1] or would require an agreement of the scientific community that has not been met yet
This does not mean that life and evolution can be understood in a deterministic way, but that having a probability different from zero for life to emerge requires specific chemical conditions. These requirements must be taken into account when tackling the questions of the origin of living systems on the early Earth or of its possible occurrence on extrasolar planetary systems, and when considering the evolution of artificial chemical systems based on dynamic kinetic stability [3,4], which constitutes one of the goals of systems chemistry [15,16]
This means that every species involved in the proto-metabolic part of Figure 1 must be located in a free energy well and protected by kinetic barriers to avoid its spontaneous fast conversion into close to equilibrium products
Summary
The main features of the living state can be identified even though a comprehensive definition of what is life may be difficult to reach [1] or would require an agreement of the scientific community that has not been met yet. Eschenmoser considered that the complexity of a reaction network involving metabolic cycles or autocatalytic networks associated with the first developments of life must have emerged from systems evolving in a chemical environment held far from equilibrium by kinetic barriers [12-14] This idea means that chemical self-organization cannot emerge when species decay with fast rates toward the equilibrium state. This idea is developed in a quantitative way to demonstrate that it can lead to valuable conclusions on the thermodynamic potential needed to bring about the living state of matter and on the nature of the corresponding processes This does not mean that life and evolution can be understood in a deterministic way, but that having a probability different from zero for life to emerge requires specific chemical conditions. These requirements must be taken into account when tackling the questions of the origin of living systems on the early Earth or of its possible occurrence on extrasolar planetary systems, and when considering the evolution of artificial chemical systems based on dynamic kinetic stability [3,4], which constitutes one of the goals of systems chemistry [15,16]
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