A new hypothesis for the origin of life

This hypothesis suggests that calcium chelating sugars, and especially ribose, have determined the nature of the first molecular systems. The self-organization capacities of these molecules enabled them to form regular arrays with certain salts. These arrays then evolved to form polysaccharides. In this first step, ribose and particularly -D-ribofuranose predominated over other prebiotic components. In a second step, the purines invaded these polysaccharides (3–5-polyribophosphodiester). The purines best suited for this were adenine and deoxyguanine, arising from the polymerization of HCN. Just as the polysaccharides reacted with purines, so the purines reacted with other small molecules and in particular, certain alkylating agents and water. After several methylation and oxidation reactions, adenine and deoxyguanine evolved to adenine, methylguanine, cytosine, uracil and thymine. Slow evolution of the prebiotic components gradually brought about a transition from a ribose world to an RNA world. The environment of this prebiotic RNA was different from that of modern RNA. For example, interaction of prebiotic RNA with water, calcium salts and certain zwitterionic molecules like the amino acids glycine and alanine was unavoidable. The interaction of these two small amino acids with calcium evolved to form transient anhydride bonds that quickly reverted to the initial state, or transformed to a peptide bond or to a more stable activated state, the oxazolone ring. The formation of this ring in double-stranded prebiotic RNA is the critical event that allowed the synthesis of new -L-amino acids. The positioning of the lateral sides of the amino acids inside the RNA suggests a stereochemical relationship that could explain the origin of the genetic code.