Chemical subsystems in PACE
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.