Question 1: Origin of Life and the Living State

Kauffman, Stuart

doi:10.1007/s11084-007-9093-2

Cited by 35 publications

(24 citation statements)

References 20 publications

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“…This was later disputed [29] by pointing out that this requires an (unrealistic) exponential growth in catalytic activity with increasing system size. Despite this criticism, the original claim (including its disputed argument) still seems to persist [30]. However, there is evidence that simple autocatalytic sets can actually be constructed experimentally [31][32][33].…”

Section: From Rna To Proteins and Dnamentioning

confidence: 99%

Autocatalytic Sets and the Origin of Life

Hordijk

Hein

Steel

2010

Entropy

165

159

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The origin of life is one of the most fundamental, but also one of the most difficult problems in science. Despite differences between various proposed scenarios, one common element seems to be the emergence of an autocatalytic set or cycle at some stage. However, there is still disagreement as to how likely it is that such self-sustaining sets could arise "spontaneously". This disagreement is largely caused by the lack of formal models. Here, we briefly review some of the criticism against and evidence in favor of autocatalytic sets, and then make a case for their plausibility based on a formal framework that was introduced and studied in our previous work.Keywords: origin of life; autocatalytic sets; RAF sets The Origin of LifeThe origin of life (OoL) remains an elusive problem, although much progress has been made in recent years. Having gone from a problem considered 'beyond science' to 'solvable in principle but maybe not in practice', many researchers now believe it will be solved in the next few decades. In fact, there are currently several OoL scenarios, but all still have some difficulties and lacunae. Although often quite different in their details, one common element which most of these scenarios have is the appearance of an autocatalytic set or cycle at some stage.Entropy 2010, 12 1734 1.1. An RNA world All life as we know it depends on a delicate interplay between DNA and proteins. However, this DNA-protein machinery seems too complex to have arisen all at once. So there appears to be a "chicken-and-egg" problem: which came first, the chicken (protein, phenotype), or the egg (DNA, genotype)?The most widely accepted resolution of this problem is that of an RNA world [1-3] preceding DNA and proteins, i.e., a collection of (self-)replicating RNA molecules, using template complementarity plus the ability to perform and catalyze their own (or each others) synthesis as a way of achieving reproduction and self-sustainability. The possibility of an RNA world has some experimental support, and is now generally considered to have been an important step in the origin of life [4,5]. However, an RNA world "spontaneously" generating proteins and DNA is not straightforward, and is certainly not (yet) proven beyond any doubt. Moreover, and perhaps more importantly, the initial appearance of an RNA world itself is still mostly an open question [2,3,6,7]. Prebiotic metabolismThe idea of a "primordial soup" [8] spontaneously generating the basic building blocks for life sounded attractive after some initial experiments along these lines [9,10], but has been much debated since then and criticized as not being capable of creating these building blocks in sufficiently large concentrations. So, there must have been something more sustainable to get anything like an RNA world started.A basic element underlying all metabolism (and therefore believed to be of very ancient origins) is the citric acid (or Krebs) cycle. This is a chemical reaction network involving a cyclic sequence of 11 substrates and reactions. It ...

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Section: From Rna To Proteins and Dnamentioning

confidence: 99%

Autocatalytic Sets and the Origin of Life

Hordijk

Hein

Steel

2010

Entropy

165

159

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“…(18,19) Also, short oligopeptides can abiotically form by aqueous condensation of amino acids, (20) especially by the salt-induced peptide formation reaction. (21) Thus, a protometabolism of geochemical reactions can have provided the ''food set'' for self-organization and further evolution of ''catalytically closed'' systems, as pioneered by Kauffman (5,22) and…”

Section: Catalytically Closed Networkmentioning

confidence: 99%

Peptide‐dominated membranes preceding the genetic takeover by RNA: latest thinking on a classic controversy

Egel

2009

BioEssays

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It is commonly presumed that abiotic membranes were colonized by proteins later on. Yet, hydrophobic peptides could have formed primordial protein-dominated membranes on their own. In a metabolism-first context, "autocatalytically closed" sets of statistical peptides could organize a self-maintaining protometabolism, assisted by an unfolding set of ribotide-related cofactors. Pairwise complementary ribotide cofactors may have formed docking guides for stochastic peptide formation, before replicating RNA emerged from this subset. Tidally recurring wet-drying cycles and an early onset of photosynthetic activities are considered most likely to meet the thermodynamic requirements. Conceivably, the earliest peptide-dominated vesicles were engaged in light harvesting, together with isoprenoid-tethered pigments, rather than providing an external boundary. Early on, the bulk of prebiotic organic matter can have formed a contiguous layer covering the mineral sediment, held in place by colloidal coherence of a hydrogel matrix. This unconventional scenario assumes a late onset of cellular individualization - perhaps from within, resembling endosporogenesis.

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“…The "metabolism first" idea suggests that life started as a system of interacting chemical cycles and the first replicators appeared later, see refs. [23,27,29,30,36,[74][75][76][77][78][79][80][81][82][83][84] for consideration of the controversy between the two concepts. Elsewhere, we have argued that the "replication first" and "metabolism first" concepts complement rather than contradict each other and have suggested that life on Earth started with a "metabolism-driven replication" [85].…”

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confidence: 99%