Metabolism First or Genes First? Investigation of Theories about the Origin of Life

Abstract

<p> Popular theories about the origin of life can be classified to two classes: metabolism first or genes first. As a metabolism first theory, the lipid world theory, in which non-covalent assemblies of lipids, such as micelles and vesicles store information in the form of a non-random molecular composition, has been proposed to investigate the possibility of inheritance without genes. Our models assume that interaction occurs between nearest neighbour molecules only, and account for spatial segregation of molecules of different types within the assembly. We also draw a distinction between a self-assembly model, in which the composition is determined by mutually favourable interaction energies between the molecules, and a catalytic model, in which the composition is determined by mutually favourable catalysis. We show that compositional inheritance occurs in both models, although the self-assembly case seems more relevant if the molecules are simple lipids. In the case where the assemblies are composed of just two types of molecules, there is a strong analogy with the classic two-allele Moran model from population genetics. This highlights the parallel between compositional inheritance and genetic inheritance. We also investigated the polymerization reactions which may bridge the gap between simple organic molecules and the beginning of the RNA world, which belongs to the class of genes first theories. We found that different from normal chemical systems, catalysts for the polymerization system can shift the equilibrium toward longer polymers. Together with RNA's potential as catalyst, the RNA polymerization system may form a feedback loop which makes the formation of functional RNA molecules easier, and come more close to the beginning of RNA world.</p>