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Dry/Wet Cycling and the Thermodynamics and Kinetics of Prebiotic Polymer Synthesis

Retired, Formerly SRI International, Menlo Park, CA 94025, USA
Department of Biomolecular Engineering, University of California, Santa Cruz, CA 95064, USA
Author to whom correspondence should be addressed.
Academic Editors: Pier Luigi Luisi and Niles Lehman
Received: 28 May 2016 / Revised: 30 June 2016 / Accepted: 11 July 2016 / Published: 26 July 2016
(This article belongs to the Special Issue The Emergence of Life: From Chemical Origins to Synthetic Biology)
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The endoergic nature of protein and nucleic acid assembly in aqueous media presents two questions that are fundamental to the understanding of life’s origins: (i) how did the polymers arise in an aqueous prebiotic world; and (ii) once formed in some manner, how were they sufficiently persistent to engage in further chemistry. We propose here a quantitative resolution of these issues that evolved from recent accounts in which RNA-like polymers were produced in evaporation/rehydration cycles. The equilibrium Nm + Nn ↔ Nm+n + H2O is endoergic by about 3.3 kcal/mol for polynucleotide formation, and the system thus lies far to the left in the starting solutions. Kinetic simulations of the evaporation showed that simple Le Châtelier’s principle shifts were insufficient, but the introduction of oligomer-stabilizing factors of 5–10 kcal/mol both moved the process to the right and respectively boosted and retarded the elongation and hydrolysis rates. Molecular crowding and excluded volume effects in present-day cells yield stabilizing factors of that order, and we argue here that the crowded conditions in the evaporites generate similar effects. Oligomer formation is thus energetically preferred in those settings, but the process is thwarted in each evaporation step as diffusion becomes rate limiting. Rehydration dissipates disordered oligomer clusters in the evaporites, however, and subsequent dry/wet cycling accordingly “ratchets up” the system to an ultimate population of kinetically trappedthermodynamically preferred biopolymers. View Full-Text
Keywords: hydrothermal ponds; RNA; kinetics; thermodynamics; polynucleotides; evaporites; molecular crowding hydrothermal ponds; RNA; kinetics; thermodynamics; polynucleotides; evaporites; molecular crowding

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Ross, D.S.; Deamer, D. Dry/Wet Cycling and the Thermodynamics and Kinetics of Prebiotic Polymer Synthesis. Life 2016, 6, 28.

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