Seminar of Physics of the Living State

(The Applied Physics Scientific Section)

(*) Summary: The origins of the genetic code have been debated between adaptive and stochastic (frozen accident) evolutionary possibilities. The specificity with which the tRNA-synthetase molecules charge tRNAs with their cognate amino-acids, and that the interaction between these molecules do not involve the anti-codon region of the tRNAs, suggested that the genetic code was determined by the co-evolution between tRNAs and synthetases precursors. I will present a model for such a system, based on chemical kinetics inside a proto-cell, considering that the tRNA precursors are short hairpin replicators (as revealed by sequence comparison) forming a hypercycle, and where rybozymes with synthetase activities catalyze the charging of the tRNAs. The chemical constants for the amino-acylations depend on the recognition of specific patterns of the tRNA hairpin sequences by the synthetases. These patterns might confuse different tRNAs, resulting in wrong amino-acylations. Natural selection, acting over a population of proto-cells, favours those with lesser mis-aminoacylations. I describe the evolution of the two different families of synthetases, which nowadays, recognize their tRNAs through two particular modes. In addition, it is possible to hypothesize which amino-acid inclusions to the early code might have been adaptive, or fixed by random selection.
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(**) Biodata: Dr. Harold P. de Vladar was born in Caracas, Republica Bolivariana de Venezuela and studied cell biology at the Central University of Venezuela, and applied mathematics (stochastic processes) at the Venezuelan Institute for Scientific Research (IVIC). He was granted a Ph.D. in “Mathematical and Natural Sciences” in 2009 by the University of Groningen, The Netherlands, where he focused on evolutionary genetics. He is currently a post-doctoral fellow at the Institute of Science and Technology Austria. He holds a permanent position at Institute of Advanced Studies (IDEA), Caracas, Venezuela. His current research interests are “Population Genetics”, the “Major Evolutionary Transitions”, and “Astrobiology”.