scholarly journals A mechanism of abiogenesis based on complex reaction networks organized by seed-dependent autocatalytic systems

2021 ◽  
Author(s):  
Zhen Peng ◽  
Jeff Linderoth ◽  
David Baum
Keyword(s):  
Dissipative System ◽  
Trophic Levels ◽  
Reaction Networks ◽  
Chemical Systems ◽  
The Core ◽  
Lower Tier ◽  
Prebiotic Chemical ◽  
The Origin Of Life ◽  
Emergence Of Life ◽  
Over Time

The core of the origin-of-life problem is to explain how a complex dissipative system could emerge spontaneously from a simple environment, perpetuate itself, and complexify over time. This would only be possible, we argue, if prebiotic chemical reaction networks had autocatalytic features organized in a way that permitted the accretion of complexity even in the absence of genetic control. To evaluate this claim, we developed tools to analyze the autocatalytic organization of food-driven reaction networks and applied these tools to both abiotic and biotic networks. Both networks contained seed-dependent autocatalytic systems (SDASs), which are subnetworks that can use a flux of food chemicals to self-propagate if, and only if, they are first seeded by some non-food chemicals. Moreover, SDASs were organized such that the activation of a lower-tier SDAS could render new higher-tier SDASs accessible. The organization of SDASs is, thus, similar to trophic levels (producer, primary consumer, etc.) in a biological ecosystem. Furthermore, similar to ecological succession, we found that higher-tier SDASs may produce chemicals that enhance the ability of the entire chemical ecosystem to utilize food more efficiently. The SDAS concept explains how driven abiotic environments, namely ones receiving an ongoing flux of food chemicals, can incrementally complexify even without genetic polymers. This framework predicts that it ought to be possible to detect the spontaneous emergence of life-like features, such as self-propagation and adaptability, in driven chemical systems in the laboratory. Additionally, SDAS theory may be useful for exploring general properties of other complex systems.

scholarly journals Autocatalytic and oscillatory reaction networks that form guanidines and products of their cyclization

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Alexander I. Novichkov ◽  
Anton I. Hanopolskyi ◽  
Xiaoming Miao ◽  
Linda J. W. Shimon ◽  
Yael Diskin-Posner ◽  
...  
Keyword(s):  
Chemical Cues ◽  
Native Chemical Ligation ◽  
Reaction Networks ◽  
Oscillatory Reaction ◽  
Experimental Conditions ◽  
Chemical Ligation ◽  
Chemical Systems ◽  
Life On Earth ◽  
Emergence Of Life ◽  
Equilibrium Chemical

AbstractAutocatalytic and oscillatory networks of organic reactions are important for designing life-inspired materials and for better understanding the emergence of life on Earth; however, the diversity of the chemistries of these reactions is limited. In this work, we present the thiol-assisted formation of guanidines, which has a mechanism analogous to that of native chemical ligation. Using this reaction, we designed autocatalytic and oscillatory reaction networks that form substituted guanidines from thiouronium salts. The thiouronium salt-based oscillator show good stability of oscillations within a broad range of experimental conditions. By using nitrile-containing starting materials, we constructed an oscillator where the concentration of a bicyclic derivative of dihydropyrimidine oscillates. Moreover, the mixed thioester and thiouronium salt-based oscillator show unique responsiveness to chemical cues. The reactions developed in this work expand our toolbox for designing out-of-equilibrium chemical systems and link autocatalytic and oscillatory chemistry to the synthesis of guanidinium derivatives and the products of their transformations including analogs of nucleobases.

scholarly journals A mechanism of abiogenesis based on complex reaction networks organized by seed-dependent autocatalytic systems

2021 ◽  
Author(s):  
Zhen Peng ◽  
Jeff Linderoth ◽  
David Baum
Keyword(s):  
Reaction Networks ◽  
Food Utilization ◽  
Complex Reaction ◽  
Chemical Systems ◽  
Promising Strategy ◽  
Underlying Basis ◽  
Scientific Questions ◽  
Emergence Of Life

The complexity gap between the biotic and abiotic worlds has made explaining abiogenesis one of the hardest scientific questions. A promising strategy for addressing this problem is to identify features shared by abiotic and biotic chemical systems that permit the stepwise accretion of complexity. Therefore, we compared abiotic and biotic reaction networks in order to evaluate the presence of autocatalysis, the underlying basis of biological self-propagation, and to see if the organization of autocatalytic motifs permits stepwise complexification. We provide an algorithm to detect seed-dependent autocatalytic systems (SDASs), namely subnetworks that can use food chemicals to self-propagate but must be seeded by some non-food chemicals to become activated. We show that serial activation of SDASs can cause incremental complexification. Furthermore, we identify life-like features that emerge during the accretion of SDASs, including the emergence of new ecological opportunities and improvements in the efficiency of food utilization. The SDAS concept explains how driven abiotic environments, namely ones receiving an ongoing flux of food chemicals, can incrementally complexify without the need for genetic polymers. This framework also suggests experiments that have the potential to detect the spontaneous emergence of life-like features, such as self-propagation and adaptability, in driven chemical systems.

scholarly journals The Grayness of the Origin of Life

Life ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 498
Author(s):  
Hillary H. Smith ◽  
Andrew S. Hyde ◽  
Danielle N. Simkus ◽  
Eric Libby ◽  
Sarah E. Maurer ◽  
...  
Keyword(s):  
Origin Of Life ◽  
Evolutionary Process ◽  
Chemical Systems ◽  
Singular Event ◽  
Prebiotic Chemical ◽  
Life Model ◽  
Life Detection ◽  
The Origin Of Life

In the search for life beyond Earth, distinguishing the living from the non-living is paramount. However, this distinction is often elusive, as the origin of life is likely a stepwise evolutionary process, not a singular event. Regardless of the favored origin of life model, an inherent “grayness” blurs the theorized threshold defining life. Here, we explore the ambiguities between the biotic and the abiotic at the origin of life. The role of grayness extends into later transitions as well. By recognizing the limitations posed by grayness, life detection researchers will be better able to develop methods sensitive to prebiotic chemical systems and life with alternative biochemistries.

scholarly journals A mechanism of abiogenesis based on complex reaction networks organized by seed-dependent autocatalytic systems

2021 ◽  
Author(s):  
Zhen Peng ◽  
Jeff Linderoth ◽  
David Baum
Keyword(s):  
Reaction Networks ◽  
Food Utilization ◽  
Complex Reaction ◽  
Chemical Systems ◽  
Promising Strategy ◽  
Underlying Basis ◽  
Scientific Questions ◽  
Emergence Of Life

The complexity gap between the biotic and abiotic worlds has made explaining abiogenesis one of the hardest scientific questions. A promising strategy for addressing this problem is to identify features shared by abiotic and biotic chemical systems that permit the stepwise accretion of complexity. Therefore, we compared abiotic and biotic reaction networks in order to evaluate the presence of autocatalysis, the underlying basis of biological self-propagation, and to see if the organization of autocatalytic motifs permits stepwise complexification. We provide an algorithm to detect seed-dependent autocatalytic systems (SDASs), namely subnetworks that can use food chemicals to self-propagate but must be seeded by some non-food chemicals to become activated. We show that serial activation of SDASs can cause incremental complexification. Furthermore, we identify life-like features that emerge during the accretion of SDASs, including the emergence of new ecological opportunities and improvements in the efficiency of food utilization. The SDAS concept explains how driven abiotic environments, namely ones receiving an ongoing flux of food chemicals, can incrementally complexify without the need for genetic polymers. This framework also suggests experiments that have the potential to detect the spontaneous emergence of life-like features, such as self-propagation and adaptability, in driven chemical systems.

scholarly journals ‘Whole Organism’, Systems Biology, and Top-Down Criteria for Evaluating Scenarios for the Origin of Life

Life ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 690
Author(s):  
Clifford F. Brunk ◽  
Charles R. Marshall
Keyword(s):  
Origin Of Life ◽  
Top Down ◽  
Chemical Systems ◽  
Biochemical Pathways ◽  
The Origin Of Life ◽  
Energy And Material Flows ◽  
Complex Scenario ◽  
Life On Earth ◽  
Physical Laws ◽  
Equilibrium Chemical

While most advances in the study of the origin of life on Earth (OoLoE) are piecemeal, tested against the laws of chemistry and physics, ultimately the goal is to develop an overall scenario for life’s origin(s). However, the dimensionality of non-equilibrium chemical systems, from the range of possible boundary conditions and chemical interactions, renders the application of chemical and physical laws difficult. Here we outline a set of simple criteria for evaluating OoLoE scenarios. These include the need for containment, steady energy and material flows, and structured spatial heterogeneity from the outset. The Principle of Continuity, the fact that all life today was derived from first life, suggests favoring scenarios with fewer non-analog (not seen in life today) to analog (seen in life today) transitions in the inferred first biochemical pathways. Top-down data also indicate that a complex metabolism predated ribozymes and enzymes, and that full cellular autonomy and motility occurred post-LUCA. Using these criteria, we find the alkaline hydrothermal vent microchamber complex scenario with a late evolving exploitation of the natural occurring pH (or Na+ gradient) by ATP synthase the most compelling. However, there are as yet so many unknowns, we also advocate for the continued development of as many plausible scenarios as possible.

Equality and Equity in Chinese Higher Education in the Post-massification Era: An Analysis Based on Chinese Scholarly Literature

2021 ◽  
pp. 1-22
Author(s):  
Qiang Zha
Keyword(s):  
Higher Education ◽  
Literature Review ◽  
Bibliometric Analysis ◽  
Chinese Higher Education ◽  
Scholarly Literature ◽  
The Core ◽  
Research Questions ◽  
Changes Over Time ◽  
Core Issues ◽  
Over Time

Abstract This paper examines several research questions relating to equality and equity in Chinese higher education via an extended literature review, which in turn sheds light on evolving scholarly explorations into this theme. First, in the post-massification era, has the Chinese situation of equality and equity in higher education improved or deteriorated since the late 1990s? Second, what are the core issues with respect to equality and equity in Chinese higher education? Third, how have those core issues evolved or changed over time and what does the evolution indicate and entail? Methodologically, this paper uses a bibliometric analysis to detect the topical hotspots in scholarly literature and their changes over time. The study then investigates each of those topical terrains against their temporal contexts in order to gain insights into the core issues.

scholarly journals What is special about L3 processing?

2013 ◽  
Vol 18 (2) ◽  
pp. 130-144 ◽  
Author(s):  
KEES DE BOT ◽  
CAROL JAENSCH
Keyword(s):  
Second Language ◽  
Language Processing ◽  
Language Use ◽  
Fundamental Question ◽  
Third Language ◽  
The Core ◽  
Dynamic Perspective ◽  
Core Issue ◽  
The Brain ◽  
Over Time

While research on third language (L3) and multilingualism has recently shown remarkable growth, the fundamental question of what makes trilingualism special compared to bilingualism, and indeed monolingualism, continues to be evaded. In this contribution we consider whether there is such a thing as a true monolingual, and if there is a difference between dialects, styles, registers and languages. While linguistic and psycholinguistic studies suggest differences in the processing of a third, compared to the first or second language, neurolinguistic research has shown that generally the same areas of the brain are activated during language use in proficient multilinguals. It is concluded that while from traditional linguistic and psycholinguistic perspectives there are grounds to differentiate monolingual, bilingual and multilingual processing, a more dynamic perspective on language processing in which development over time is the core issue, leads to a questioning of the notion of languages as separate entities in the brain.

Parameters or cues?

2004 ◽  
Vol 7 (1) ◽  
pp. 35-36 ◽  
Author(s):  
BRIAN MACWHINNEY
Keyword(s):  
Second Language ◽  
Second Language Acquisition ◽  
Language Acquisition ◽  
Hebbian Learning ◽  
Universal Grammar ◽  
Back Propagation ◽  
Parameter Setting ◽  
Functional Categories ◽  
The Core ◽  
Over Time

Truscott and Sharwood Smith (henceforth T&SS) attempt to show how second language acquisition can occur without any learning. In their APT model, change depends only on the tuning of innate principles through the normal course of processing of L2. There are some features of their model that I find attractive. Specifically, their acceptance of the concepts of competition and activation strength brings them in line with standard processing accounts like the Competition Model (Bates and MacWhinney, 1982; MacWhinney, 1987, in press). At the same time, their reliance on parameters as the core constructs guiding learning leaves this model squarely within the framework of Chomsky's theory of Principles and Parameters (P&P). As such, it stipulates that the specific functional categories of Universal Grammar serve as the fundamental guide to both first and second language acquisition. Like other accounts in the P&P framework, this model attempts to view second language acquisition as involving no real learning beyond the deductive process of parameter-setting based on the detection of certain triggers. The specific innovation of the APT model is that changes in activation strength during processing function as the trigger to the setting of parameters. Unlike other P&P models, APT does not set parameters in an absolute fashion, allowing their activation weight to change by the processing of new input over time. The use of the concept of activation in APT is far more restricted than its use in connectionist models that allow for Hebbian learning, self-organizing features maps, or back-propagation.

Solar-flare exposure and thermoluminescence of Luna 24 core material

1980 ◽  
Vol 297 (1428) ◽  
pp. 41-50 ◽  
Keyword(s):  
Solar Flare ◽  
Core Material ◽  
Substantial Fraction ◽  
Natural Radiation ◽  
Mixing Properties ◽  
Local Component ◽  
The Core ◽  
Radiation History ◽  
Solar Flare Tracks ◽  
Over Time

Mineral grains from three depths within the Luna 24 drill core ( ca . 90, 125 and 196 cm) have been examined for solar-flare tracks. Large proportions (55-100%) of grains from all three levels are found to be track-rich (with central track densities p e > 10 8 cm -2 ), and a substantial fraction ( ca . 25-50%) of all grains display trackdensity gradients. These observations indicate that most of the mineral grains have been cycled through the top ca . 1 mm of the lunar surface at some time in their history. Some degree of submaturity is observed towards the bottom of the core. The most likely depositional model envisages rapid infall of highly irradiated material into a less mature local component with rather little subsequent reworking. Thermoluminescence (t.l.) studies indicate a lower natural radiation dose in samples from the 196 cm level compared with those from the two upper levels. This can result either from random variations in the local internal radioactivity or from mixing properties of the pre-irradiated material over time scales of less than ca . 100 ka. Radiation sensitization of samples suggests a possible use of t.l. sensitivity for the interpretation of lunar radiation history.

The Development of Xunzi’s Theory of Xing, Reconstructed on the Basis of a Textual Analysis of Xunzi 23, “Xing E” 性惡 (Xing is Bad)

Early China ◽  
2001 ◽  
Vol 26 ◽  
pp. 99-158 ◽  
Author(s):  
Dan Robins
Keyword(s):  
Human Nature ◽  
Textual Analysis ◽  
Detailed Examination ◽  
The Core ◽  
Over Time

The section of the Xunzi called “Xing e” 性惡 (xing is bad) prominently and repeatedly claims that people's xing is bad. However, no other text in the Xunzi makes this claim, and it is widely thought that the claim does not express Xunzi's fundamental ideas about human nature. This article addresses the issue in a somewhat indirect way, beginning with a detailed examination of the text of “Xing e”: identifying a core text, removing a series of interpolations, analyzing the structure of the core text, and distinguishing between three positions that are defended there. This analysis shows that the claim that people's xing is bad is not really central to “Xing e.” More ambitiously, it supports the conclusion that Xunzi's ideas about people's xing changed over time. Though Xunzi did claim that people's xing is bad, he later abandoned the claim, and replaced it with an account of wei 偽 “artifice.”

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