This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
[{'content': "Which of the following is not true about buffering action of haemoglobin (Hb)? \nSelect and explain. \nA. Hb is technically intracellular buffer, B. Hb is functionally a plasma buffer, C. Hb's buffering action is due to its histidine content, D. Oxygenated Hb is a strong base", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Protein buffers in blood include haemoglobin (150g/l) and plasma proteins (70g/l). Buffering is by the imidazole group of the histidine residues which has a pKa of about 6.8. This is suitable for effective buffering at physiological pH. Haemoglobin is quantitatively about 6 times more impoant than the plasma proteins as it is present in about twice the concentration and contains about three times the number of histidine residues per molecule.', 'role': 'assistant'}]