Simultaneous origin of homochirality, the genetic code and its directionality

Abstract

The origin of homochirality in molecules characterizing living systems has remained a mystery since Pasteur's recognition of the problem some 150 years ago.(2-5) Most theories also assume that homochirality emerged in one class of molecules (e.g. ribose) from which it was enriched in other molecules (e.g. amino acids) as well.(2-5)I propose a novel, experimentally testable hypothesis describing a process by which selective chirality in amino acids and ribonucleotides emerged simultaneously and hand-in-hand with the origin and directionality of the genetic code within a system of interactions involving amino acids, peptides, nucleotide bases, their sugars and polynucleotides.

Emergence of Life from Multicomponent Mixtures of Chemicals: The Case for Experiments with Cycling Physicochemical Gradients

“…The progenotic individuals (Woese and Fox, 1977) that preceded and may have coexisted with LUCAs (Doolittle, 1999) could be described as ''structurally imperfect prokaryotes,'' possibly with a mechanically weak cell envelope, living in proto-biofilms in a non-Darwinian evolutionary world, when non-Darwinian horizontal gene transfer was the main mechanism for sharing emerging genetic information before biological lineages were established 408 SPITZER (Woese et al, 1990;Woese, 1998Woese, , 2000Woese, , 2002. The progenotes were likely still coevolving protoribosomal protein syntheses, genetic protocodes and their crowded vectorial protometabolic reactions (Root-Bernstein, 2007)-a life that we may not recognize today; they were likely a part of non-homeostatic proto-biofilm systems, being organized and maintained by oscillating diurnal gradients. From the progenote world, a few populations of LUCAs came out as ''evolutionary winners'' with a fixed genetic code and a more efficient and enlarged ribosome (Fox, 2010(Fox, , 2011, representing life as we know it today.…”

Experimental Test of L- and D-Amino Acid Binding to L- and D-Codons Suggests that Homochirality and Codon Directionality Emerged with the Genetic Code

“…If that were not true, then the codons ACG and GCA would encode the same amino acids rather than different ones. I, however, have suggested previously that during the evolution of the genetic code, translation direction may have been ambiguous [4,5]. Specificity of amino acid binding to codons of opposite directionality therefore becomes a problem in need of experimental testing.…”

“…Thus, evidence for an asymmetric force would create a new problem, which would be why that force is manifested in living systems exclusively. I have therefore spent many years [4] attempting to rethink the problem of homochirality and have recently [5] recognized an assumption (usually, though not always, unstated) that homochirality emerged before the code itself. But what if homochirality was not established before the genetic code emerged?…”

“…But what if homochirality was not established before the genetic code emerged? I began exploring the implications of this unexplored possibility and two years ago proposed a radically different hypothesis: the reason that homochirality and an essentially universal genetic code both characterize living organisms may be that they arose as a function of each other [5].…”

Possible Physical Mechanisms in the Galaxy to Cause Homochiral Biomaterials for Life

“…(g) Work on the RNA world and the homochirality of biomolecules is promising. See, for example, Reference [39][40][41]. Recently, there has been increasing interest in the chiral nature or handedness of biomolecules.…”