Chemical subsystems in PACE

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Design of chemical subsystems en route to artifical cells constituted, arguably, the most challenging task within the PACE project. The implementation was guided by two theoretical models of protocells, the Ganti's chemoton model in which an autocatalytic metabolism is coupled to the self-reproduction of a membrane and a genetic subsystem [1], and the Los Alamos protocell model, which explicitly considers elementary events in template replication, coupled to micelle reproduction and energy uptake from a photochemical engine [5]. The latter model requires that the genetic material is stably associated with the lipid container (relative to the generation (replication) time of the protocell), such that a strong connection between geno- and phenotype is maintained. Furthermore, a coupling between the genetic template and the metabolic chemistry is envisaged as this would allow selection and evolution on the genetic material on the basis of metabolic performance. Interaction of the genetic material with the lipid container and ultimately embedding the genetic material within the lipid phase is critical for this concept.

In both implementations, the protocell integration efforts have been done in stepwise manner i.e., exploring protocellular subsystems or three formal couplings: a metabolic - genetic coupling, a genetic - membrane coupling and a metabolic - membrane coupling.