On the prebiotic synthesis of nucleobases, nucleotides, oligonucleotides, pre-RNA and pre-DNA molecules

All the strategies for the prebiotic syntheses of RNA and DNA assume the adequate availability of the presumptive precursors such as purine and pyrimidine nucleic bases, nucleosides and nucleotides. Polymerization of activated nucleotides probably furnished the first informational oligonucleotides. The formation of these precursors from mixtures of simple gases was shown to occur in a variety of conditions including UV-irradiation, electric discharge, heating, volcanic activity and marine vents. Even though a well-defined physical chemical scenario on the primitive Earth is not available, prebiotic syntheses were most probably performed using the simplest chemicals and the most common conditions present at that time. During these synthetic processes minerals played the relevant role of catalysts furnishing local microenvironments for the selective concentration of reagents and for the preservation of newly formed products. Here we focus on the optimal experimental conditions needed to carry out these syntheses and on the characterization of the major products thus obtained. Special attention will be addressed to catalyzed processes. Taken together, these procedures and data suggest novel scenarios for the molecular evolution of life on the primitive Earth and may provide a chemical clue to the evaluation of the plausible emergence of extraterrestrial forms of life