What is the prehistory of amino acids in cells?
Edward N. Trifonov is a professor at the Institute of evolution at University of Haifa, Israel. One of the main research topics in his group is the reconstruction of the origins of life. In one of his papers, The triplet Code From First Principles, he proposes the the chronological appearance of the 20 amino acids. There are a lot of hypothesis and testable predictions, among which is the theory of S. Miller that some biological compounds have been abiotically produced in the atmosphere. This prediction has been confirmed by imitation experiments, yielding ten different amino acids, as glycine and alanine being the prevalent ones.

The author tries to predict the chronological order in which the 20 amino acids appeared by taking into account various criteria (studies, hypothesis and viewpoints) that propose some order, as each one of them contributes to the consensus order to a certain extent. This contribution is described in the form of rank. He compiles a list of 60 rankings of 60 different criteria to derive the consensus order. Some of the criteria are:


  N1’. Criteria based on various evaluations of complexity of amino-acids. N1, N34, N35,
  N37 – as in (5), and N44 (6). G, A, S, P, V, C, D, T, N, L, K, I, E, (MQ), H, R, F, Y, W
  
  N2’. Criteria based on evolution of amino-acyl-tRNA synthetases. N2, N7 (5).
  (AG), (DFHKNPST), (CEILMQRV), (WY)
  
  N4’. Criteria based on amino-acid compositions of various sets of presumably ancient
  proteins. N4, N26 (5), N41 (7), N45 (8), N47 (9), N48 (10), and N58 (11).


The first ten (earliest) consensus amino acids are the same as in Millers’s experiments. The amino acids appeared last have their respective codons borrowed from already existing ones. The derived consensus order is G, A, D, V, P, S, E, (L, T), R, (I, Q, N), H, K, C, F, Y, M, W.

The author also proposes a reconstruction of the chronological order in which the 64 codons had appeared.