User:Galapah/sandbox/Molecular evolution by Edward Trifonov

The molecular evolution
In 1996 Thomas Bettecken, a German geneticist noticed that most of the triplet expansion diseases can be attributed only to two triplets: GCU and GCC, all the rest being their permutations or complementary counterparts. He discussed this finding with Trifonov, his friend and colleague. Trifonov had earlier discovered (GCU)n to be a hidden mRNA consensus sequence. Thus the combination of these two facts led them to the idea that the (GCU)n could reflect a pattern of ancient mRNA sequences.

The first triplets
Since GCU and GCC appeared to be the most expandable (or the most “agressive”) triplets, Trifonov and Bettecken inferred that they could be the first two codons. Their ability to expand rapidly comparing to other triplets would provide them with evolutionary advantage. Single point mutations of these two would give rise to 14 other triplets.

Consensus temporal order of amino acids
Having the suspected first two triplets, they pondered which amino acids appeared the first, or more generally in which order all the proteinogenic amino acids emerged. To address this question, they resorted to three, according to them the most natural, hypotheses: Later on, Trifonov collected even 101 criteria for the amino acids order. Each criterion could be represented as a vector of length 20 (for 20 basic amino acids). Trifonov averaged over all of them (gave the same weight to all of them) and got the proposed temporal order of the amino acids emergence: • # glycine
 * 1) The earliest amino acids were chemically the simplest.
 * 2) They would be present among the products of the Miller-Urey experiment.
 * 3) They would be associated with the older one of the two known classes of aminoacyl-tRNA synthetases.

• # alanine

• # aspartic acid

• # valine

• # proline

• # serine

• # glutamic acid

• # leucine

• # threonine

• # isoleucine

• # arginine

• # asparagine

• # glutamine

• # lysine

• # histidine

• # phenylalanine

• # cysteine

• # methionine

• # tyrosine

• # tyrosine

Predictions

 * 1) The first proteins were glycine-rich.
 * text
 * 1) The earliest protein sequences were a mosaic of two independent alphabets.
 * text
 * 1) ... the third prediction
 * text
 * 1) ... the fourth prediction
 * text