遗传密码包含遗传编码的氨基酸的字母。十个阶段1氨基酸,包括Gly,阿拉,Ser,Asp,Glu,Val,Leu,Ile,Pro和Thr,可以从益生元环境中获得,而10个阶段2氨基酸,包括Phe,Tyr,Arg,他的,Trp,Asn,Gln,Lys,Cys,和Met,只有后来才能从氨基酸生物合成中获得。在古细菌中,已知最古老的生物,20个氨基酸的标准字母为“冷冻”,随后的3个Gyrs中没有编码其他氨基酸。四十年前,人们发现密码被冻结了,因为所有的生物体都很好地适应了标准氨基酸,以至于形成了寡基因屏障,由完全依赖于标准代码的基因组成,从密码中删除任何一个氨基酸都会导致生存力丧失。一旦确定了密码冻结的原因,程序是由世界各地的科学家设计的,以使新型非规范氨基酸(ncAA)的编码成为可能。这些编码的阶段3ncAA现在超过了代码中的20个规范的阶段2氨基酸。
The genetic code contains an alphabet of genetically encoded amino acids. The ten Phase 1 amino acids, including Gly, Ala, Ser, Asp, Glu, Val, Leu, Ile, Pro and Thr, were available from the prebiotic environment, whereas the ten Phase 2 amino acids, including Phe, Tyr, Arg, His, Trp, Asn, Gln, Lys, Cys, and Met, became available only later from amino acid biosyntheses. In the archaeon Methanopyrus kandleri, the oldest organism known, the standard alphabet of 20 amino acids was \"frozen\" and no additional amino acid was encoded in the subsequent 3 Gyrs. Four decades ago, it was discovered that the code was frozen because all the organisms were so well adapted to the standard amino acids that oligogenic barriers, consisting of genes that are thoroughly dependent on the standard code, would cause loss of viability upon the deletion of any one amino acid from the code. Once the reason for the freezing of the code was ascertained, procedures were devised by scientists worldwide to enable the encoding of novel noncanonical amino acids (ncAAs). These encoded Phase 3 ncAAs now surpass the 20 canonical Phase 2 amino acids in the code.