Origin & Evolution of Life

Protobiotic Network Reproducers Are Compositional Attractors: Enhanced Probability for Life’s Origin

By Keith Cowing
Status Report
January 17, 2023
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Protobiotic Network Reproducers Are Compositional Attractors: Enhanced Probability for Life’s Origin
Models of mutually catalytic networks. The figure depicts three models that share the basic structure of a mutually catalytic network, whereby each molecule type (circle) may exert catalysis on some others (arrows). The network properties are displayed in the central row: (A) In the GARD model (26) the size of circles indicates graded concentrations of one of the different compound, and the arrow thickness denotes graded catalytic intensity, both varying over several orders of magnitude. (B) In the basic Collectively Autocatalytic Set (CAS) model (10) (see disambiguation on the term autocatalytic (73)) concentrations are not specified (drawn as equal circle size) and catalytic intensity is assumed to be Boolean, without defining graded catalytic intensities, hence arrows all have the same width. (C) In the model of Kamimura and Kaneko (11), shown here in simplified form, the catalytic power varies in a limited interval and the momentary molecular concentrations within a cell are all equal. The top row provides information on the model’s mode of containment: being within a lipid phase such as a micelle or a bilayer, hence defined as an integral part of the catalytic network (A); Enclosed in an implicit container without molecular identity or transport properties (B); Enclosed by a molecularly undefined cellular entity with specified molecular transport. In the bottom row shows how the three models are different in the depicting the environmental food molecules: In (A), food molecules catalytically accrete into a lipid assembly (i), becoming part of the network and participating in catalyzed oligomerizations (ii) (32). The latter facet is also true for (B), except that there is no catalyzed food entry; hence, the rate of food entry is not kinetically coupled to network dynamics, a synchronization mechanism necessary from full reproduction (31). Such separation is even more noticeable in (C), where there is a clear distinction between food and network molecules. More specifically, every molecule in the network is obligatorily produced in from a food non-catalytic precursor. As shown in both (i) and (ii), a network member Xj catalyzes a reaction in which a new copy of a network molecule Xi is produced from a food molecule S. The net stoichiometric reaction is XI+S2Xi, considered catalyzed replication of a network molecule, employing a monomolecular reaction from a food molecule to a catalytic member of the network (SXi). We note that such stoichiometric replication of each individual component does not guarantee selfreproduction of the network as a whole (15). Such single molecule self-copying is also not equivalent to autocatalysis (circular arrows in (A) and (B)) which may contribute to assembly self-reproduction as part of the entire mutually catalytic matrix (15). — chemrxiv.org

The origin of life must have involved an unlikely transition from chaotic chemistry to reproducing supramolecular structures.

Previous quantitative analyses of reproducing mutually catalytic networks made of simple molecules have led to increasing popularity of this pre-RNA scenario for life’s origin. Here, we investigate in detail the reproduction characteristic of the GARD computer-simulated physicochemically rigorous lipid-based model.

This model displays compatibility with heterogeneous environments, addresses the network’s spatial demarcation, and portrays trans-generational compositional information transfer. However, we find that compositionally reproducing states are extremely rare, suggesting that random roaming would be a vastly inefficient path towards reproduction. Rewardingly, further scrutiny shows that all self-reproducing states are also dynamic attractors of the catalytic network.

This suggests a greatly enhanced propensity for the spontaneous emergence of reproduction and primal evolution, vastly augmenting the likelihood of protolife appearance.

Amit Kahana Weizmann Institute of Science – Department of Molecular Genetics
Lior Segev Weizmann Institute of Science – Department of Physics Core Facilities
Doron Lancet Weizmann Institute of Science – Department of Molecular Genetics

Full paper https://chemrxiv.org/engage/chemrxiv/article-details/625c0ea711b146242525ad37


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