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First published 20 July 2015

Chemical Architectures for Self-Replicating Proto-Cells

Erwan Bigan, Jean-Marc Steyaert, and St├ęphane Douady

Abstract (Excerpt)

Two questions arise when considering chemical architectures for cellular life: (i) are specific features such as cycles, auto-catalysis or metabolic closure required? (ii) how can chemical insulation between the inside and the outside be achieved?

We show that self-replication of a chemical system is possible without any explicit feature, and without the need for their emergence through complexity. We use a simple generic proto-cell model, whereby conservative chemical reactions occur within a membrane resulting from the self-assembly of one of the chemical species (membrane precursor), with this membrane being semi-permeable by diffusion to some other species (nutrient). We have mathematically proven simple minimal conditions pertaining only to the topology of the em-bedded chemical reaction network (CRN), and relying upon the concepts of moieties and siphons. Moities are conserved quantities and siphons are subsets of species whose absence cannot be compensated by the chemical reactions. A necessary condition for stationary growth is that each moiety must be fed. And a sufficient condition is that each siphon be fed (Bigan et al., 2014). Generating random CRNs with arbitrary stoichiometry, we find that these conditions are typically reached at a relatively low complexity, with a number of reactions only slightly above the number of species (Bigan et al., 2015b). When the necessary condition is met but the sufficient one is not, the proto-cell may reach a stationary growth regime or not depending on the kinetics of pass reactions, connecting a siphon to its complement and transferring mass into the siphon.