Autocatalytic Sets and the Origin of Life

Abstract

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 ...

Required Levels of Catalysis for Emergence of Autocatalytic Sets in Models of Chemical Reaction Systems

“…The idea of autocatalytic sets as a precursor to life has certainly not been without criticism [17–19], but recent (exciting) experimental evidence shows that they are a real possibility [20–24]. Thus, we believe that our theoretical and computational studies and results are of direct relevance in the larger context of the origin of life [5,25,26]. …”

“…Note (as already stated earlier [26]) that this notion of an autocatalytic set is somewhat different from the (chemical) term autocatalytic reaction in which a molecule directly catalyzes its own production. With an autocatalytic set we do not mean a set of autocatalytic reactions, but rather a set of molecules and reactions which is collectively autocatalytic in the sense that all molecules help in producing each other (through mutual catalysis, and supported by a food set).…”

“…Autocatalytic sets may have played an important role in the origin of life [5,15,26,27], and are a necessary, although not sufficient, condition for life. Here, autocatalytic sets are defined more formally as RAF sets as follows (see [1,2] for the full mathematical definition and notations).…”

Beyond Descartes and Newton: Recovering life and humanity

“…A second view is that life started with budding hollow lipid vessicles called liposomes, which do occur, (Daemer and Barchfield). A third view is the spontaneous emergence of sets of molecules, say RNA or small proteins called peptides, or both, which mutually catalyze one antoher's formation from some outside building blocks, (Kauffman 1971, 1986, 1995, Hordijk et al, 2010. Call these collectively autocataltyic sets.…”

Approaches to the Origin of Life on Earth

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