This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Mutations & Codons, Subject name: Biochemistry
[{'content': 'Which of the following is a Nonsense codon : \nSelect and explain. \nA. UAG, B. AUG, C. AGG, D. UUA', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Non-sense codons/Terminator Codons/Punctuator codons Codons which do not code for any paicular amino acid. Mark end of protein synthesis. These codons are UAA UAG UGA UGA is a stop codon; But in special circumstances, it stands for seleno-cysteine ("21st" amino acid). UAG is a stop codon; But in special circumstances, it stands for pyrrolysine (22nd amino acid)', 'role': 'assistant'}]