This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
[{'content': 'Which of the following can be a homologous substitution for valine in hemoglobin? \nSelect and explain. \nA. Isoleucine, B. Glutamic acid, C. Phenylalanine, D. Lysine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: In Many examples of Point Mutations The classic example is sickle-cell disease, which is caused by mutation of a single base out of the 3 x 109 in the genome, a T-to-A DNA substitution, which in turn results in an A-to-U change in the mRNA corresponding to the sixth codon of the b-globin gene. The altered codon specifies a different amino acid (valine rather than glutamic acid), and this causes a structural abnormality of the b-globin molecule leading to hemoglobin aggregation and red blood cell "sickling." Ref: Harper\'s Illustrated Biochemistry, 30E (2015) Pg no 460.', 'role': 'assistant'}]