This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'Amino acids not coded by triplet codona) Lysineb) Hydroxyprolinec) Selenocysteined) Pyrrolysinee) Ornithine \nSelect and explain. \nA. be, B. ad, C. bc, D. ce', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Selenocysteine is 21st AA coded by UGA which is normally a stop codon.\nPyrrolysine is 22nd AA coded by UGA which is also a stop codon normally.\nLysine is also an essential amino acid so has to be coded by codon (AAA, AAG).\nHydroxyproline and hydroxylysine are not coded by a codon, i.e. they are not incorporated into protein during translation. Rather, they are formed in protein, by post-translational modification (hydroxylation) of proline and lysine, respectively.\n"Ornithine is not an amino acid coded for by DNA, and, in that sense, is not involved in protein synthesis.', 'role': 'assistant'}]