Metabolism in the Origin of Life
Prof. Robert Shapiro (New York University)
In one widely accepted theory of the development of life on Earth, evolution began with the appearance of organic polymers with the ability to catalyze their own replication. By natural selection, these polymers evolved into an RNA world and then into a DNA/ protein world. This theory does not explain, however, the processes by which the unorganized, diverse mixtures of small organic chemicals produced by abiotic processes were converted into highly organized, functional polymers. Some experimenters have attempted to mimic the process by carrying out multi-step syntheses using pure reagents, controlled conditions and sophisticated equipment. But the odds that these detailed procedures would be duplicated in the absence of scientists and laboratories are insignificant.
A remedy for this conceptual gap lies in a hypothesis called “metabolism-first”: The first steps of self-organization were driven by the flow of available free energy through an appropriate chemical mixture confined within a natural compartment or on a surface. One key requirement is that the energy be made available, or coupled to the system in a way that promotes self-organization. This can be visualized by considering a cycle of chemical reactions that contains a “driver” reaction – one that interacts with the external energy source in a way that is favored by thermodynamics. Material would be drawn into this cycle in order to maximize the discharge of free energy. The cycle would adapt to environmental changes to maintain this process, and in doing so evolve into a network of increasing complexity which eventually produces a replicator.