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': "At isoelectric pH protein: \nSelect and explain. \nA. Have Net charge 'O', B. Are positively charged, C. Are negatively charged, D. Don't migrate", 'role': 'user'}, {'content': 'Answer: A \nExplanation: At physiological pH (7.4), all amino acids have both a negatively charged carboxyl ion (C00-)and a positively charged ammonium ion (-NH3). The amino acids are therefore dipolar ion (Zwitter ions)', 'role': 'assistant'}]