Concept for a minimal chemoton

Given the conclusion that the Chemoton in Figure 1 has to be an extreme heterotroph and that the resource molecule (XA ) has to be structurally complex for any Chemoton-inspired protocell of rather limited dynamic complexity, one may ask what essentials of the theory can be seen as translatable into chemistry. We aimed at chemical self-replication (1.2.1) stoichimetrically coupled to lipid formation (Figure 2) and saw a minimal chemoton as follows:

  1. A non-autocatalytic metabolic subsystem running outside of the cell and providing the environment of the cell with a high excess of precursor molecules, from which both, templates and lipids can be synthesized.
  2. A self-replicating genetic subsystem ultimatively running inside the cell. This is the autocatalytic driving force.
  3. Membrane-bound lipid generation stoechiometrically coupled to membrane-bound self-replication, ultimatively releasing templates to the interior. Stoechiometric coupling simply means a mechanism by which: nLipids = f ⋅ nTemplates, f ≥ 1

Theoretical considerations on the amplification factor f (1.2.2) show that 1000 to 10000 lipids need to be generated per template, if the cell is a giant unilamelar vesicle. An implemenation of the full version of such a minimal chemoton would thus require a dual role of the catalipid, acting as both, as a leaving group during template formation as well as a nucleophilic or acid-base catalyst in the hydrolysis of precursor lipids (such as anhydrides of fatty acids) to fatty acids. The former aspect was to be addressed in PACE.