That is the chance for in silico simulation studies, which are apt at exploring the evolutionary dynamics involved in the origin of life. Obviously, such concomitant emergence, if ever occurred, should have been an evolutionary process–with ongoing transitions over a period of time, which is difficult to investigate by pure lab work.
However, actually, the possibility of ‘homochirality arising together with biopolymers’ cannot be ruled out (see for a discussion). Surely, considering that homochirality is so important for the genetic and functional roles of biopolymers, the feasibility that homochirality arose after the emergence of the biopolymers should be discarded. Unfortunately, many years of efforts along this line have not led to any convincing conclusion–actually, there are quite a lot of hypotheses or speculations many of those experimental results are yet far from being relevant to the biomonomers (see for recent reviews). It was believed such asymmetry, if initially not in regard of, should have ultimately brought about chirality-bias on ‘biomonomers’ (i.e., nucleotides and amino acids), which would then assemble into corresponding biopolymers with uniform chirality. That is, the focus has been placed upon investigating plausible physic-chemical mechanisms that may have led to prebiotic environments asymmetric in chirality. Just because people realized that homochirality is crucial to biopolymers, almost all previous studies in this area assumed that homochirality originated before the emergence of biopolymers. However, the origin of homochirality is an exception–as mentioned above, it is ‘straightforward and inevitable’, such that apparently more attention has been paid to this issue than to other ones concerning the origin of life. In this field, relevant issues are often not clearly defined.
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The origin of life is a field full of controversies, which is not surprising when considering we have not even reached a consensus on the definition of life. This brings up a significant sub-problem, i.e., the origin of homochirality, for the problem of the origin of life.
However, in a prebiotic chemical world, the small molecules from which these macromolecules could be synthesized tend to have existed as racemic mixtures (that is, with equal quantities of the two chiral types). Genetic polymers (DNA/RNA) must be composed of residues with the same chirality (handedness) to be able to act as template in replication functional polymers (proteins/RNA) must be composed of residues with the same chirality to be able to fold into appropriate structures. By modelling the evolutionary process, the present computer simulation study provides significant clues for experiments in future. The process is actually not only an issue of chemistry but also an issue involving evolution–thus previously difficult to reveal by pure lab work in this area.
Here we demonstrate, by in silico simulation, that instead, the required chirality-deviation may have been established along with the emergence of biopolymers at the beginning stage in the origin of life–just deriving from a chirality-symmetric monomer pool. Now that life should have originated from a prebiotic non-life background, how could this dissymmetry have occurred? Previous studies in this area focused their efforts on how the chirality-symmetry may have been broken at the monomer level (i.e., nucleotides or amino acids), but have achieved little advance over decades of years. People have long been curious about the fact that central molecules in the living world (biopolymers), i.e., nucleic acids and proteins, are asymmetric in chirality (handedness), but as the relevant background, the chemical world is symmetric in chirality. In other words, the results suggest that the homochirality may have originated along with the advent of biopolymers during the origin of life, rather than somehow at the level of monomers before the origin of life. Here we show, by computer simulation–with a model based on the RNA world scenario, that the biased-chirality may have been established at polymer level instead, just deriving from a racemic mixture of monomers (i.e., equally with the two chiral types). For many years, people have focused on exploring plausible physic-chemical mechanisms that may have led to prebiotic environments biased to one chiral type of monomers (e.g., D-nucleotides against L-nucleotides L-amino-acids against D-amino-acids)–which should have then assembled into corresponding polymers with homochirality, but as yet have achieved no convincing advance. How homochirality concerning biopolymers (DNA/RNA/proteins) could have originally occurred (i.e., arisen from a non-life chemical world, which tended to be chirality-symmetric) is a long-standing scientific puzzle.
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