Figure 2.

The bottom-up approach research strategies. (A) Each protocell component (vide infra) can be investigated in “isolation” to better understand the various processes pertaining to its synthesis/formation: information polymer, functional catalysts or self-assembly/stability of the compartment. (B) A higher degree of complexity can be attained by using chemicals that by themselves already link to two component functions: for instance, metal complexes that can harvest light (here a ruthenium tris(bipyridine) and catalyse reactions, or polymers such RNA ribozymes that are both genotype (information component) and phenotype (catalyst). (C) The systems approach offers insight into the increased level of cooperativity necessary to grasp the complexity of living interactions. The creation of chemical gradients, for example, requires the presence of a compartment and an energy harvesting system. In the case of PAHs, which are sparingly soluble in water, the compartment boundary not only allows for a distinction between two aqueous volumes, it also increases the availability of the PAH molecules by providing a specific hydrophobic environment for their solubilization, thereby improving the energy conversion.