title: Evolutionary processes possibly limiting the kinds of amino acids in protein to twenty: a review.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D005075:Biological Evolution; D003062:Codon; D005815:Genetic Code; D008954:Models, Biological; D014176:Protein Biosynthesis; D012641:Selection, Genetic; D013379:Substrate Specificity
chemical_list: D000596:Amino Acids; D003062:Codon