The study of the origins of life on Earth is confronted with the crucial question of the transition 0 from complex prebiotic chemistry to simple biology corresponding to the first Darwinian evolutionary assemblages. The discovery of plausible pathways capable of ensuring this transition has become a major challenge in evolutionary biochemistry. Molecular biology, by highlighting the extraordinary diversity of the RNA molecule, in particular its catalytic properties in the form of ribozymes, underlines the probable existence of a past RNA world, a biochemical world that would have preceded the contemporary DNA-RNA-protein world. It is, however, very difficult to synthesize (i.e. manufacture in the laboratory) RNA under so-called "prebiotic" conditions. Alternative, robust genetic systems that could have served as templates for the synthesis of today's RNAs are under investigation. These early motifs were able to exert their properties, genotypically by simple "directed synthesis" and phenotypically due to great plasticity, and with the help of metal or ribonucleotide cofactors already widespread on the primitive Earth. Last but not least, the spatial localization of the first processes may have been facilitated by encapsulation processes, enabling us to imagine and design integrated protocell models on an experimental scale.
The exploration of a series of ribonucleic acid motifs found in certain viruses or in present-day viroids, capable of reversible self-cutting and thus of shaping their own genome, sheds new light on what may have been the first steps in biological catalysis. Are these species fossils of an ancient RNA world? Are these motifs capable of withstanding the extreme conditions of temperature, pressure and salinity that would have prevailed in the first ages of life?
In this seminar, we will retrace the main stages in the natural history of life, at the molecular level and in the light of the latest data from prebiotic chemistry and modern molecular and structural biology.
