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Wozniak K, Brzezinski K. Biological Catalysis and Information Storage Have Relied on N-Glycosyl Derivatives of β-D-Ribofuranose since the Origins of Life. Biomolecules 2023; 13:biom13050782. [PMID: 37238652 DOI: 10.3390/biom13050782] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 04/24/2023] [Accepted: 04/29/2023] [Indexed: 05/28/2023] Open
Abstract
Most naturally occurring nucleotides and nucleosides are N-glycosyl derivatives of β-d-ribose. These N-ribosides are involved in most metabolic processes that occur in cells. They are essential components of nucleic acids, forming the basis for genetic information storage and flow. Moreover, these compounds are involved in numerous catalytic processes, including chemical energy production and storage, in which they serve as cofactors or coribozymes. From a chemical point of view, the overall structure of nucleotides and nucleosides is very similar and simple. However, their unique chemical and structural features render these compounds versatile building blocks that are crucial for life processes in all known organisms. Notably, the universal function of these compounds in encoding genetic information and cellular catalysis strongly suggests their essential role in the origins of life. In this review, we summarize major issues related to the role of N-ribosides in biological systems, especially in the context of the origin of life and its further evolution, through the RNA-based World(s), toward the life we observe today. We also discuss possible reasons why life has arisen from derivatives of β-d-ribofuranose instead of compounds based on other sugar moieties.
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Affiliation(s)
- Katarzyna Wozniak
- Department of Structural Biology of Prokaryotic Organisms, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-074 Poznan, Poland
| | - Krzysztof Brzezinski
- Department of Structural Biology of Prokaryotic Organisms, Institute of Bioorganic Chemistry, Polish Academy of Sciences, Noskowskiego 12/14, 61-074 Poznan, Poland
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2
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Lehman NE, Kauffman SA. Constraint Closure Drove Major Transitions in the Origins of Life. ENTROPY (BASEL, SWITZERLAND) 2021; 23:E105. [PMID: 33451001 PMCID: PMC7828513 DOI: 10.3390/e23010105] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2020] [Revised: 01/05/2021] [Accepted: 01/11/2021] [Indexed: 12/21/2022]
Abstract
Life is an epiphenomenon for which origins are of tremendous interest to explain. We provide a framework for doing so based on the thermodynamic concept of work cycles. These cycles can create their own closure events, and thereby provide a mechanism for engendering novelty. We note that three significant such events led to life as we know it on Earth: (1) the advent of collective autocatalytic sets (CASs) of small molecules; (2) the advent of CASs of reproducing informational polymers; and (3) the advent of CASs of polymerase replicases. Each step could occur only when the boundary conditions of the system fostered constraints that fundamentally changed the phase space. With the realization that these successive events are required for innovative forms of life, we may now be able to focus more clearly on the question of life's abundance in the universe.
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Affiliation(s)
- Niles E. Lehman
- Edac Research, 1879 Camino Cruz Blanca, Santa Fe, NM 87505, USA;
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Smail BA, Clifton BE, Mizuuchi R, Lehman N. Spontaneous advent of genetic diversity in RNA populations through multiple recombination mechanisms. RNA (NEW YORK, N.Y.) 2019; 25:453-464. [PMID: 30670484 PMCID: PMC6426292 DOI: 10.1261/rna.068908.118] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/21/2018] [Accepted: 01/14/2019] [Indexed: 06/09/2023]
Abstract
There are several plausible abiotic synthetic routes from prebiotic chemical materials to ribonucleotides and even short RNA oligomers. However, for refinement of the RNA World hypothesis to help explain the origins of life on the Earth, there needs to be a manner by which such oligomers can increase their length and expand their sequence diversity. Oligomers longer than at least 10-20 nucleotides would be needed for raw material for subsequent natural selection. Here, we explore spontaneous RNA-RNA recombination as a facile means by which such length and diversity enhancement could have been realized. Motivated by the discovery that RNA oligomers stored for long periods of time in the freezer expand their lengths, we systematically investigated RNA-RNA recombination processes. In addition to one known mechanism, we discovered at least three new mechanisms. In these, one RNA oligomer acts as a splint to catalyze the hybridization of two other oligomers and facilitates the attack of a 5'-OH, a 3'-OH, or a 2'-OH nucleophile of one oligomer onto a target atom of another. This leads to the displacement of one RNA fragment and the production of new recombinant oligomers. We show that this process can explain the spontaneous emergence of sequence complexity, both in vitro and in silico.
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Affiliation(s)
- Benedict A Smail
- Department of Chemistry, Portland State University, Portland, Oregon 97207, USA
| | - Bryce E Clifton
- Department of Chemistry, Portland State University, Portland, Oregon 97207, USA
| | - Ryo Mizuuchi
- Department of Chemistry, Portland State University, Portland, Oregon 97207, USA
| | - Niles Lehman
- Department of Chemistry, Portland State University, Portland, Oregon 97207, USA
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Yarus M. Eighty routes to a ribonucleotide world; dispersion and stringency in the decisive selection. RNA (NEW YORK, N.Y.) 2018; 24:1041-1055. [PMID: 29785967 PMCID: PMC6049501 DOI: 10.1261/rna.066761.118] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Accepted: 05/10/2018] [Indexed: 06/08/2023]
Abstract
We examine the initial emergence of genetics; that is, of an inherited chemical capability. The crucial actors are ribonucleotides, occasionally meeting in a prebiotic landscape. Previous work identified six influential variables during such random ribonucleotide pooling. Geochemical pools can be in periodic danger (e.g., from tides) or constant danger (e.g., from unfavorable weather). Such pools receive Gaussian nucleotide amounts sporadically, at random times, or get varying substrates simultaneously. Pools use cross-templated RNA synthesis (5'-5' product from 5'-3' template) or para-templated (5'-5' product from 5'-5' template) synthesis. Pools can undergo mild or strong selection, and be recently initiated (early) or late in age. Considering >80 combinations of these variables, selection calculations identify a superior route. Most likely, an early, sporadically fed, cross-templating pool in constant danger, receiving ≥1 mM nucleotides while under strong selection for a coenzyme-like product, will host selection of the first encoded biochemical functions. Predominantly templated products emerge from a critical event, the starting bloc selection, which exploits inevitable differences among early pools. Favorable selection has a simple rationale; it is increased by product dispersion (SD/mean), by selection intensity (mild or strong), or by combining these factors as stringency, reciprocal fraction of pools selected (1/sfsel). To summarize: chance utility, acting via a preference for disperse, templated coenzyme-like dinucleotides, uses stringent starting bloc selection to quickly establish majority encoded/genetic expression. Despite its computational origin, starting bloc selection is largely independent of specialized assumptions. This ribodinucleotide route to inheritance may also have facilitated 5'-3' chemical RNA replication.
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Affiliation(s)
- Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado Boulder, Boulder, Colorado 80309-0347, USA
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Mariani A, Russell DA, Javelle T, Sutherland JD. A Light-Releasable Potentially Prebiotic Nucleotide Activating Agent. J Am Chem Soc 2018; 140:8657-8661. [PMID: 29965757 PMCID: PMC6152610 DOI: 10.1021/jacs.8b05189] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2018] [Indexed: 12/17/2022]
Abstract
Investigations into the chemical origin of life have recently benefitted from a holistic approach in which possible atmospheric, organic, and inorganic systems chemistries are taken into consideration. In this way, we now report that a selective phosphate activating agent, namely methyl isocyanide, could plausibly have been produced from simple prebiotic feedstocks. We show that methyl isocyanide drives the conversion of nucleoside monophosphates to phosphorimidazolides under potentially prebiotic conditions and in excellent yields for the first time. Importantly, this chemistry allows for repeated reactivation cycles, a property long sought in nonenzymatic oligomerization studies. Further, as the isocyanide is released upon irradiation, the possibility of spatially and temporally controlled activation chemistry is thus raised.
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Affiliation(s)
| | | | - Thomas Javelle
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge
Biomedical Campus, Cambridge CB2 0QH, U.K.
| | - John D. Sutherland
- MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge
Biomedical Campus, Cambridge CB2 0QH, U.K.
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Puthenvedu D, Majerfeld I, Yarus M. Non-Watson-Crick RNA synthesis suited to origin functions. RNA (NEW YORK, N.Y.) 2018; 24:90-97. [PMID: 29042506 PMCID: PMC5733574 DOI: 10.1261/rna.063974.117] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Accepted: 10/11/2017] [Indexed: 06/02/2023]
Abstract
A templated RNA synthesis is characterized in which G5'pp5'G accelerates synthesis of A5'pp5'A from pA and chemically activated ImpA precursors. Similar acceleration is not observable in the presence of UppU, CppC, AppG, AppA, or pG alone. Thus, it seems likely that AppA is templated by GppG via a form or forms of G:A base-pairing. AppA also appears, more slowly, via a previously known untemplated second-order chemical route. Such AppA synthesis requires only ordinary near-neutral solutions containing monovalent and divalent salts, and rates are only slightly sensitive to variation in pH. Templated synthesis rates are first order in pA, ImpA, and template GppG; thus third order overall. Therefore, this reaction resembles cross-templating of AppA on poly(U), but is notably slower and less sensitive to temperature. Viewing AppA as a coenzyme analog, GppG templating provides a simpler molecular route, termed para-templating, to encoded chemical functions. Para-templating can also arise from a single, localized nucleobase geosynthetic event which yields purines. It requires only a single backbone-forming chemistry. Thus it may have appeared earlier and served as evolutionary precursor for more complex forms of encoded genetic expression.
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Affiliation(s)
- Deepa Puthenvedu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Boulder, Colorado 80309-0347, USA
| | - Irene Majerfeld
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Boulder, Colorado 80309-0347, USA
| | - Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Boulder, Colorado 80309-0347, USA
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Yarus M. Efficient Heritable Gene Expression Readily Evolves in RNA Pools. J Mol Evol 2017; 84:236-252. [PMID: 28669113 PMCID: PMC5501911 DOI: 10.1007/s00239-017-9800-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 06/24/2017] [Indexed: 11/25/2022]
Abstract
Heritable gene expression arises readily in a simple non-genetic system employing known small-RNA biochemistry. Pooled cross-templating ribonucleotides show varied chemical competence on which selection acts, even calculating only minimal effects. Evolution can be quick-computed progress toward encoded gene expression can require only days or weeks for two millimolar, partly activated complementary 5' ribonucleotides. After only one product selection cycle, early templating can become prevailing pool behavior. Subsequently, a selected templated product is efficiently amplified as a pool ages, frequently accumulated in the same order of concentration as incoming nucleotides. Pools spontaneously favor templating because sporadic nucleotide accumulations increase it-and selection increases templating in pools of all ages. Nonetheless, templated chemical competence appears most easily in young pools. Pool history is critical-pools can perish from periodic hazards (like tides), or alternatively, from hazards roughly constant in time (like rainfall). Selection is greatly enhanced in constant hazard pools-more effective if pools have varied ages. Stronger selection is disproportionately more effective. Selected evolutionary change has an uncomplicated molecular basis-progress from chemical product synthesis to templated, proto-genetic inheritance exploits identity between templating and entropic catalysis. Though discovered by computation, selection of an elevated product of template catalysis is plausible, independent of any chemical or mathematical assumption. Selected chemical variation before genetics (chance utility) therefore inaugurates inheritance, even when hindered by unstable, dilute nucleotides, erratically supplied in undependable quantities. Remarkably, such uncontrolled conditions are not necessarily hostile, but can instead accelerate appearance of primordial gene-like behavior.
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Affiliation(s)
- Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO, 80309-0347, USA.
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Abstract
Given two primordial conditions that seem likely to be common, near-ideal reactions for evolutionary progress are realized. These requisites are sporadic availability of pooled reactants and evolutionarily useful products within a pool’s repertoire. These intrinsically optimizing circumstances function without genetics, and therefore can help evolve a first genetic system. This process is termed chance utility.
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Majerfeld I, Puthenvedu D, Yarus M. Cross-backbone templating; ribodinucleotides made on poly(C). RNA (NEW YORK, N.Y.) 2016; 22:397-407. [PMID: 26759450 PMCID: PMC4748817 DOI: 10.1261/rna.054866.115] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2015] [Accepted: 12/02/2015] [Indexed: 06/02/2023]
Abstract
G(5')pp(5')G synthesis from pG and chemically activated 2MeImpG is accelerated by the addition of complementary poly(C), but affected only slightly by poly(G) and not at all by poly(U) and poly(A). This suggests that 3'-5' poly(C) is a template for uncatalyzed synthesis of 5'-5' GppG, as was poly(U) for AppA synthesis, previously. The reaction occurs at 50 mM mono- and divalent ion concentrations, at moderate temperatures, and near pH 7. The reactive complex at the site of enhanced synthesis of 5'-5' GppG seems to contain a single pG, a single phosphate-activated nucleotide 2 MeImpG, and a single strand of poly(C). Most likely this structure is base-paired, as the poly(C)-enhanced reaction is completely disrupted between 30 and 37 °C, whereas slower, untemplated synthesis of GppG accelerates. More specifically, the reactive center acts as would be expected for short, isolated G nucleotide stacks expanded and ordered by added poly(C). For example, poly(C)-mediated GppG production is very nonlinear in overall nucleotide concentration. Uncatalyzed NppN synthesis is now known for two polymers and their complementary free nucleotides. These data suggest that varied, simple, primordial 3'-5' RNA sequences could express a specific chemical phenotype by encoding synthesis of complementary, reactive, coenzyme-like 5'-5' ribodinucleotides.
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Affiliation(s)
- Irene Majerfeld
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
| | - Deepa Puthenvedu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
| | - Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
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10
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Crucial steps to life: From chemical reactions to code using agents. Biosystems 2016; 140:49-57. [DOI: 10.1016/j.biosystems.2015.12.007] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Revised: 12/05/2015] [Accepted: 12/07/2015] [Indexed: 01/21/2023]
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Puthenvedu D, Janas T, Majerfeld I, Illangasekare M, Yarus M. Poly(U) RNA-templated synthesis of AppA. RNA (NEW YORK, N.Y.) 2015; 21:1818-25. [PMID: 26272215 PMCID: PMC4574757 DOI: 10.1261/rna.052696.115] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 07/20/2015] [Indexed: 06/02/2023]
Abstract
Simple nucleotide templating activities are of interest as potential primordial reactions. Here we describe the acceleration of 5'-5' AppA synthesis by 3'-5' poly(U) under normal solution conditions. This reaction is apparently templated via complementary U:A base-pairing, despite the involvement of two different RNA backbones, because poly(U), unlike other polymers, significantly stimulates AppA synthesis. These interactions occur in moderate (K(+)) and (Mg(2+)) and are temperature sensitive, being more efficient at 10°C than at 4°C, but absent at 20°C. The reaction is only slightly pH sensitive, despite potentially relevant substrate pKa's. Kinetic data explicitly support production of AppA by interaction of stacked 2MeImpA and pA nucleotides paired with a single molecule of U template. At a lower rate, AppA can also be produced by a chemical reaction between 2MeImpA and pA, without participation of poly(U). Molecular modeling suggests that 5'-5' joining between stacked or concurrently paired A's can occur without major departures from normal U-A helical coordinates. So, coenzyme-like 5'-5' purine dinucleotides might be readily synthesized from 3'-5' RNAs with complementary sequences.
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Affiliation(s)
- Deepa Puthenvedu
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
| | - Teresa Janas
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA Department of Biotechnology and Molecular Biology, University of Opole, 45-032 Opole, Poland
| | - Irene Majerfeld
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
| | - Mali Illangasekare
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
| | - Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
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Strazewski P. Omne Vivum Ex Vivo … Omne? How to Feed an Inanimate Evolvable Chemical System so as to Let it Self-evolve into Increased Complexity and Life-like Behaviour. Isr J Chem 2015. [DOI: 10.1002/ijch.201400175] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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13
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Fontecilla-Camps JC. The stereochemical basis of the genetic code and the (mostly) autotrophic origin of life. Life (Basel) 2014; 4:1013-25. [PMID: 25522252 PMCID: PMC4284479 DOI: 10.3390/life4041013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 11/27/2014] [Accepted: 12/11/2014] [Indexed: 01/25/2023] Open
Abstract
Spark-tube experiments and analysis of meteorite contents have led to the widespread notion that abiotic organic molecules were the first life components. However, there is a contradiction between the abundance of simple molecules, such as the amino acids glycine and alanine, observed in these studies, and the minimal functional complexity that even the least sophisticated living system should require. I will argue that although simple abiotic molecules must have primed proto-metabolic pathways, only Darwinian evolving systems could have generated life. This condition may have been initially fulfilled by both replicating RNAs and autocatalytic reaction chains, such as the reductive citric acid cycle. The interactions between nucleotides and biotic amino acids, which conferred new functionalities to the former, also resulted in the progressive stereochemical recognition of the latter by cognate anticodons. At this point only large enough amino acids would be recognized by the primordial RNA adaptors and could polymerize forming the first peptides. The gene duplication of RNA adaptors was a crucial event. By removing one of the anticodons from the acceptor stem the new RNA adaptor liberated itself from the stereochemical constraint and could be acylated by smaller amino acids. The emergence of messenger RNA and codon capture followed.
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Affiliation(s)
- Juan C Fontecilla-Camps
- Metalloproteins Unit, University Grenoble Alpes, Institut de Biologie Structurale, F-38044 Grenoble, France.
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Hernandez AF, Grover MA. A necessary condition for coexistence of autocatalytic replicators in a prebiotic environment. Life (Basel) 2013; 3:403-20. [PMID: 25369813 PMCID: PMC4187171 DOI: 10.3390/life3030403] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2013] [Revised: 06/13/2013] [Accepted: 06/17/2013] [Indexed: 11/30/2022] Open
Abstract
A necessary, but not sufficient, mathematical condition for the coexistence of short replicating species is presented here. The mathematical condition is obtained for a prebiotic environment, simulated as a fed-batch reactor, which combines monomer recycling, variable reaction order and a fixed monomer inlet flow with two replicator types and two monomer types. An extensive exploration of the parameter space in the model validates the robustness and efficiency of the mathematical condition, with nearly 1.7% of parameter sets meeting the condition and half of those exhibiting sustained coexistence. The results show that it is possible to generate a condition of coexistence, where two replicators sustain a linear growth simultaneously for a wide variety of chemistries, under an appropriate environment. The presence of multiple monomer types is critical to sustaining the coexistence of multiple replicator types.
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Affiliation(s)
- Andres F Hernandez
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
| | - Martha A Grover
- School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
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Yarus M. A ribonucleotide Origin for Life--fluctuation and near-ideal reactions. ORIGINS LIFE EVOL B 2013; 43:19-30. [PMID: 23344886 PMCID: PMC3576565 DOI: 10.1007/s11084-013-9325-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2012] [Accepted: 01/03/2013] [Indexed: 12/22/2022]
Abstract
Oligoribonucleotides are potentially capable of Darwinian evolution - they may replicate and can express an independent chemical phenotype, as embodied in modern enzymatic cofactors. Using quantitative chemical kinetics on a sporadically fed ribonucleotide pool, unreliable supplies of unstable activated ribonucleotides A and B at low concentrations recurrently yield a replicating AB polymer with a potential chemical phenotype. Self-complementary replication in the pool occurs during a minority (here ≈ 35 %) of synthetic episodes that exploit coincidental overlaps between 4, 5 or 6 spikes of arbitrarily arriving substrates. Such uniquely productive synthetic episodes, in which near-ideal reaction sequences recur at random, account for most AB oligonucleotide synthesis, and therefore underlie the emergence of net replication under realistic primordial conditions. Because overlapping substrate spikes are unexpectedly frequent, and in addition, complex spike sequences appear disproportionately, a sporadically fed pool can host unexpectedly complex syntheses. Thus, primordial substrate fluctuations are not necessarily a barrier to Darwinism, but instead can facilitate early evolution.
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Affiliation(s)
- Michael Yarus
- Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, CO 80309-0347, USA.
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