second position Many amino UUU UCU he UUC ucc ser uac y ucc cysg acids are UAA'I stop UGA stop A eu specific ed by UUG UCG UAG stop UGG TrpG more than CUU CCU CUC CCC CAU His cG U CUA CCA Arg& aone codon CUG CCG 0cc翼 degeneracy AUU ACU AAU AGU Asn AUC lle m(简并性) ACC AAC AGC Thr AUA ACA AAA AGA Codons AUGt Met ACG AAG AGG ArgG GCU GAU GGU u specifying GCC Asp GGC Val the same GUA GCA GAA GAA GUG GCG GAG Glu G amino acid Chain-terminating or"nonsense" codons t Also used in bacteria to specify the initiator formyl-Met-tRNA Met are called TABLE 15-1 synonyms The genetic code 同义密码子Many amino acids are specified by more than one codon￾degeneracy (简并性). Codons specifying the same amino acid are called synonyms (同义密码子). TABLE 15-1 The Genetic Code