This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
[{'content': 'Sickle cell disease is present with which mutation: \nSelect and explain. \nA. Cross-linked defect, B. Base pair defect, C. Mismatch defect, D. Base pair substitution', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. (d) Base pair substitutionRef: Harper's Biochemistry, 30th ed. pg. 416-17A partial missense mutation (type of base pair substitution) glutamic acid, the normal amino acid in position 6 of the b chain, has been replaced by valine.", 'role': 'assistant'}]