Using sophisticated computational methods, scientists from the Earth-Life Science Institute (ELSI) at the Tokyo Institute of Technology, explored the "chemical neighborhood" of nucleic acid analogs. Surprisingly, they found well over a million variants 1 Are DNA and RNA the only way to store this information? Or are they perhaps the best way? "There are two kinds of nucleic acids in biology. We wanted to know if there is one more to be found or even a million more. The answer is, there seem to be many, many more. The remarkable thing is, among the incredible variety of organisms on Earth, these two molecules are essentially the only ones biology uses.
Biologists and chemists have long wondered why this should be. Are these the only molecules that could perform this function? If not, are they perhaps the best?
Chemical space is, in principle, unlimited as at least one more atom can almost always be added to any given structure. 2 Any given structure space is limited by the input definitions, as well as by defined structural constraints. As our principal concern was the elucidation of the size of prebiotically accessible nucleic acid structure space, we limited ourselves to C, H, O, and N as structural atoms for the core. One could also include greater numbers of various other elements.
My comment: It becomes evident, that there is basically no constraint, why nucleobases could not incorporate any element like sulfur, oxygen, nitrogen, etc. of the periodic table.
One might expect that molecules with smaller connected Carbon components should be easier for abiotic chemistry to explore. We therefore computed the largest connected carbon−carbon run among these isomers ( isomers are ions or molecules with identical formulas but distinct arrangements of atoms in space ) . According to this analysis, the natural ribosides and deoxyribosides inhabit a fairly redundant ( superfluous, unnecessary, needless) and nonminimal region of this space.
My comment: This is a remarkable find and implicitly leads to design. There would be no reason why stochastic events would generate complex, rather than simple, and minimal carbon arrangements. Nor is there physical necessity that says that the arrangement should be so. This is evidence that directing intelligent agency is the most plausible explanation. The chemistry space is far too vast to select by chance the right finely-tuned functional arrangement.
Is it remarkable, given the existence of this structure space, that biology found a solution to the need for information storage? The large number of possible motifs, both those which have thus-far been synthesized, which represent a miniscule fraction of the possible ones (as demonstrated here, whether one considers compositional or stereoisomer space), argue that solutions in this chemical space should be discoverable in multiple ways by evolvable systems.
My comment: Here the authors insert once again, without justification, the evolutionary canard as their explanation. Why? Because there is no other feasible alternative to design. The problem is, they smuggle evolutionary vocabulary to where it does not belong. Evolution plays no role in abiogenesis.
From the standpoint of xeno and synthetic biology, could other, perhaps equally good, or even better genetic systems be devised? The answer to this question will require sophisticated and protracted chemical experimentation. Studies to date suggest that the answer could be no. Many nearly as good, some equally good, and a few stronger base-pairing analogue systems are known.
My comment: Amazing!! RNA and DNA are probably an OPTIMALLY DESIGNED genetic system. This is clear evidence of design.
2. One Among Millions: The Chemical Space of Nucleic Acid-Like Molecules
The genetic code is one in a million
if we employ weightings to allow for biases in translation, then only 1 in every million random alternative codes generated is more efficient than the natural code. We thus conclude not only that the natural genetic code is extremely efficient at minimizing the effects of errors, but also that its structure reflects biases in these errors, as might be expected were the code the product of selection.