Life originated as a genetic code (contribution to the discussion of the paper by G R Ivanitskii “21st century: what is life from the perspective of physics” [Usp. Fiz. Nauk. 180 337 (2010); Phys. Usp. 53 327 (2010); Usp. Fiz. Nauk. 182 1235 (2012); Phys. Usp. 55 1152 (2012); Usp. Fiz. Nauk 182 1238 (2012); Phys. Usp. 55 1155 (2012)])

This letter is aimed at concretizing the origin-of-life scenario. The author defines life as a self-reproducing information system and briefly discusses the current status of the origin-of-life problem. The first bimolecular origin-of-life scenario is proposed, which is based on the interaction between amino acids and triplets of nucleotides corresponding to their codons. In this scenario, the reproduction of information occurred by hydrogen bonding with complementary nucleotides and, hence, was due to the formation of complementary codons that reproduced the primary codon. The bimolecular scenario fundamentally necessitates the existence of complementary codons for all those of amino acids associated with life. A complete correspondence is shown to exist between codons and complementary codons for 21 amino acids, a fact which greatly favors the proposed hypothesis, because this correspondence is impossible if amino acids choose codons at random.