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': 'Marble bone disease, characterized by increased bone density is due to mutation in the gene encoding \nSelect and explain. \nA. Carbonic anhydrase I, B. Carbonic anhydrase II, C. Carbonic anhydrase III, D. Carbonic anhydrase IV', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Osteopetrosis\xa0 (marble\xa0 bone\xa0 disease),\xa0 characterized\xa0 by increased bone density, is a rare condition characterized by\xa0 inability\xa0 to\xa0 resorb\xa0 bone.\xa0 One\xa0 form\xa0 occurs\xa0 along\xa0 with\xa0 renal tubular acidosis and cerebral calcification. It is due to mutations\xa0 in\xa0 the\xa0 gene\xa0 (located\xa0 on\xa0 chromosome\xa0 8q22) encoding carbonic anhydrase II (CA II), one of four isozymes of carbonic anhydrase present in human tissues. In osteoclasts involved in bone resorption, CA II apparently provides protons to neutralize the OH−\xa0 ions left inside the cell when H+\xa0 ions are pumped across their ruffled borders.\nThus, if CA II is deficient in activity in osteoclasts, normal bone resorption does not occur, and osteopetrosis results. The mechanism of the cerebral calcification is not clear, whereas the renal tubular acidosis reflects deficient activity of CA II in the renal tubules.\nHarper, Ed 30, Pg No 642, 643', 'role': 'assistant'}]