Combinatorial chemistry in the prebiotic environment

Orateur : David DEAMER (Department of Biomolecular Engineering, University of California, Santa Cruz CA 95064)

The pathway leading to the origin of life presumably included a process by which polymers were synthesized abiotically from simpler compounds on the early Earth, then encapsulated to form protocells. Previous studies have reported that clay mineral surfaces can concentrate and organize activated mononucleotides, thereby promoting their polymerization into RNA-like molecules. However, a plausible prebiotic activation mechanism has not been established, and minerals cannot form cellular compartments. We are exploring ways in which non-activated mononucleotides can undergo polymerization and encapsulation, and particularly the possibility that such reactions can be promoted by an organizing matrix. The organizing agents we are investigating include multilamellar liquid crystals and crystallization of monovalent salts, both of which force a solute into orderly arrays. We found that RNA-like polymers are synthesized by a condensation reaction when mixtures of amphiphilic lipids and mononucleotides are exposed to cycles of dehydration and rehydration. The lipids concentrate and organize the monomers within multilamellar liquid-crystalline matrices that self-assemble in the dry state. The chemical potential driving the polymerization reaction is supplied by the anhydrous conditions in which water becomes a leaving group, with heat providing activation energy. Significantly, upon rehydration the polymeric products can be encapsulated in trillions of microscopic compartments. Each compartment is unique in its composition and contents, and can be considered to be an experiment in a natural version of combinatorial chemistry that would be ubiquitous in the prebiotic environment. A successful experiment would be a compartment that captured a system of polymers capable of catalyzing their own replication. If this can be reproduced in the laboratory, it would represent a significant step toward understanding the origin of cellular life.

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