(Kempes et al. 2017, Klump et al. 2020). Of course this will also be the case where nonsense is stored and the ‘ones’ and the ‘zeros’ mean nothing. The Δg will still be positive to store this. The objection may be raised that just as this can happen with a man-made computer, the same can happen with the DNA in biological systems. Mutations will be stored just like other genuine coding parts of the DNA. The reply is that this indeed will be the case. This will continue even as mutations increase, but there will be a limit when the very machinery for performing the data storage is itself affected, which then means the living system disintegrates and the DNA bonds break up, since the organization of specific pathways such that Δg > 0 levels are kept in the numerous locations, cannot be sustained. Klump, et al. (2020) have estimated the values of the free energy Δg that each triplet of the nucleotides T C A G (that is Thymine, Cytosine, Adenine and Guanine) is held at, and thus the “uphill” energy required, in order to form each triplet – see Table 1. These Δg values are in kJ/mol triplet, so in order to get some idea of a very rough comparison with the Landauer value, one can divide by Avogadro’s number (6.02 x 1023), to get a crude estimate as to the approximate energy for each triplet. So, the lowest free energy of the table is that required for stabilizing ATA and TAT which is 11.7 kJ/mol triplet which translates approximately to 19.4 x 10-21 J/triplet, which is approximately 6.5 times the Landauer value for a bit of information (3 x 10-21 J/bit). The highest Δg value in the chart is that for stabilizing GCG and CGC which is 24.3 kJ/mol triplet, and this translates approximately to 40.3 x 10-21 J/triplet and thus approximately 13 times the Landauer value for a bit of information. The factor of 6.5 or 13 will in fact be less since the Landauer value for the triplet will be larger than for 1 bit of information, but it gives a rough order of magnitude estimate. Nevertheless, this is a significant amount of energy that must be injected into the system along a very precise pathway to cause each of these 64 DNA triplet codons to form and to be maintained in this non-equilibrium state. In a surprising flight of fancy Klump et al. (2020) argue that such large and stable bonds are formed by an evolutionary process! In the abstract of their paper they write … one can envision the genetic code as composed of interlocking thermodynamic cycles that allow codons to ‘evolve’ from each other through a series of sequential transitions and transversions, which are influenced by an energy landscape modulated by both thermodynamic and kinetic factors. As such, early evolution of the genetic code may have been driven, in part, by differential energetics, as opposed exclusively by the functionality of any gene product. In such a scenario, evolutionary pressures can, in part, derive from the optimization of biophysical properties (e.g. relative stabilities and relative rates), in addition to the classic perspective of being driven by a phenotypical adaptive advanTable 1. Genetic code matrix for human mitochondrial DNA showing the triplet of codons (nucleotides) which codes for the 20 amino acids listed in the key, and showing for each triplet the free energy Δg for that triplet (and its associated duplex) expressed in kJ/mol triplet, as reported by Klump et al. (2020). 1st T C A G 3rd T 14.6 Phe 13.4 Ser 11.7 Tyr 13.4 Cys T 15.9 Phe 18.4 Ser 13.4 Tyr 19.3 Cys C 12.5 Leu 14.2 Ser 12.6 STOP 14.2 Trp A 16.3 Leu 18.8 Ser 13.4 STOP 18.4 Trp G C 15.5 Leu 18.0 Pro 15.5 His 18.4 Arg T 16.7 Leu 23.0 Pro 17.2 His 24.3 Arg C 13.4 Leu 18.4 Pro 16.3 Gln 18.0 Arg A 17.2 Leu 23.4 Pro 17.2 Gln 23.4 Arg G A 13.8 Ile 13.0 Thr 13.8 Asn 13.0 Ser T 15.1 Ile 18.0 Thr 15.5 Asn 18.8 Ser C 11.7 Met 13.4 Thr 14.6 Lys 13.4 Arg A 15.5 Met 18.4 Thr 15.5 Lys 18.0 Arg G G 15.5 Val 18.8 Ala 15.1 Asp 18.0 Gly T 16.7 Val 23.9 Ala 16.7 Asp 23.9 Gly C 13.4 Val 19.3 Ala 15.9 Glu 18.4 Gly A 17.2 Val 24.3 Ala 16.7 Glu 23.0 Gly G kj/mol triplet kj/mol triplet kj/mol triplet kj/mol triplet Key: Ala Arg Asn Asp Cys Glu Gln Gly His Ile Alanine Arginine Asparagine Aspartic Acid Cysteine Glutamic Acid Glutamine Glycine Histidine Isoleucine Leu Lys Met Phe Pro Ser Thr Trp Tyr Val Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine MCINTOSH Language, codes, & interaction with thermodynamics 2023 ICC 321
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