This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Basics of amino acids, Subject name: Biochemistry
[{'content': 'What is Isoelectric point? \nSelect and explain. \nA. When pH = pI, B. When zwitterion exists, C. Protein precipitation occurs, D. All', 'role': 'user'}, {'content': "Answer: D \nExplanation: At Isoelectric pH (pI), protein's net charge is 0, known as Zwitterion. This structure is insoluble, so precipitates. At Acidic pH, protein has positive charge. At Alkaline pH, protein has negative charge.", 'role': 'assistant'}]