This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
One molecule of Hb can bind to a maximum number of 
Select and explain. 
A. Two molecules of oxygen, B. One molecule of oxygen, C. Four molecules of oxygen, D. Six molecules of oxygen
C: Four molecules of oxygen
Answer: C: Four molecules of oxygen 
Explanation: Hemoglobins bind four molecules of O2 per tetramer, one per heme. A molecule of O2 binds to a hemoglobin tetramer more readily if other O2 molecules are already bound.Reference: Harper&;s Biochemistry; 30th edition; Chapter 6; Proteins: Myoglobin & Hemoglobin