Compositional Lipid Assemblies as Evolving Protocells

Life is complex, and its origin is about how sufficient chemical complexity emerged to afford replication. A crucial aspect of replication is the faithful transmission of sufficient information to progeny. The graded autocatalysis replication domain (GARD) model, in the realm of the lipid world scenario, offers a possible route for such pursuit. In this framework, non-covalent assemblies of amphiphiles, such as lipid micelles or vesicles, can acquire adequate endogenous complexity, mediated by a set of catalyzed chemical reactions akin to metabolism. Our computer simulations show that GARD assemblies carry and transmit compositional information through catalyzed homeostatic growth followed by random fission.

Key in GARD dynamics are composomes, spontaneously-forming replication-prone quasi-stationary states. A group of composomes, gleaned by clustering, is termed compotype, and may be regarded as species in the framework of lipid world and GARD. Indeed, such GARD species were recently shown to display a significant measure of Darwinian evolution, and their populations are capable of displaying ecological dynamics. Thus, the GARD formalism allows one to delineate a well-defined chemically-rigorous path from random chemical environments (“primordial soup”) to replicating and evolving protocellular structures.