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  1. The smallest bistable chemical system and the origin of life

    Thomas Wilhelm, Institute of Food Research, Norwich, UK

    30 November 2009

    The smallest bistable chemical system and the origin of life

    Thomas Wilhelm

    1971 was a remarkable year. Surely for different reasons (you might have been born then), but one reason is that three people presented the idea of self-organization and autocatalytic cycles as the possible origin of life [1-3]. They did this completely independent of each other, time was simple ripe, it was a nice coincidence. None of them can claim being the first, maybe it was somebody else. Robert Rosen (cited in [1], not in [2,3]) discussed essentially the same idea earlier [4]. Following Rosen’s approach, Letelier et al. presented a “minimal (three-step) autocatalytic set” [5].

    However, I would argue that “The smallest chemical reaction system with bistability” [6] is the smallest autocatalytic set only comprising elementary chemical reactions. The system feeds upon just one outer substrate. Catalyzed by the internal metabolite Y, another internal metabolite X is produced from S. X is then transformed to Y. This reaction is catalysed by X. Thus, the production of X and Y is cross-catalysed by the other metabolite, respectively. This autocatalytic set also shows a remarkable robustness: even if one metabolite (catalyst) would run out completely, just the presence of the other already secures functioning. With only Y present, X will be produced, and with only X present, Y will be produced.

    So life might have been originated from the following very simple scenario: it could have been started with an elementary autocatalytic set, such as the smallest bistable chemical system. Then more and more additional compounds and reactions could have been integrated successively, until complex ancient “real” metabolisms emerged. This would have been a simple straightforward way of evolution, in a sense more plausible then one big phase-transition of sudden autocatalytic closure [3].

    [1] O.E. Roessler (1971) Ein systemtheoretisches Modell zur Biogenese. (in German) Z. fuer Naturforschung 26b(8), 741-746.
    [2] M. Eigen (1971) Selforganization of matter and the evolution of biological macromolecules. Naturwissenschaften 58(10), 465-523.
    [3] S.A. Kauffman (1971) Cellular homeostasis, epigenesist and replication in randomly aggregated macromolecular systems. J. Cybernetics 1, 71-96.
    [4] R. Rosen (1958) A relational theory of biological systems. Bull. Math. Biophys. 20, 245-341.
    [5] J.-C. Letelier et al. (2006) Organizational invariance and metabolic closure: analysis in terms of (M,R) systems. J. Theor. Biol. 238, 949-961.
    [6] T. Wilhelm (2009) The smallest chemical reaction system with bistability. BMC Syst. Biol. 3, 90.
    [7] The Schloegl system is smaller, but not elementary, cf. [6].

    Competing interests

    no competing interests