The 21st and 22nd Amino Acid

Qiu Wenyuan, Deng Wenye, Cai Yanqiao, ^#Yan Ruiqing
(Department of Chemistry, State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000)
( ^#Lanzhou Maternity and Child Health Hospital, Lanzhou 730030)

Abstract This article introduces the undiscovered two amino acids¾ ¾ the 21st amino acid and the 22nd amino acid, which are called selenocysteine and pyrrolysine, respectively. They are nonstandard amino acids and directly encoded by genetic codes. Their RNA nucleotide triplets are UGA and UAG, respectively. The encoding way of these two amino acids, which are different from those twenty standard amino acids, lead to the problem of codon redefinition.
Key words Amino acid, Selenocysteine, Pyrrolysine, UAG codon, UGA codon