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
In a hemoglobin molecule which of the following is a homologous substitution for valine? 
Select and explain. 
A. Isoleucine, B. Glutamic acid, C. Phenylalanine, D. Lysine
B: Glutamic acid
Answer: B: Glutamic acid 
Explanation: Valine can be replaced by glutamic acid. At position number 67 in the amino acid sequence, three different amino acid substitutions have been found in different varient hemoglobins. Hb Sydney Valine - Alanine; Hb M Milwaukee Valine - Glu; & Hb Bristol Val - Asp. All of these are functionally normal hemoglobin types. Ref: Harper's Biochemistry, 26th Edition, Page 362 ; Color Atlas of Genetics By Eberhard Passarge, 2007, Page 348