Bisphosphoglyceric acid (BPG) is a byproduct of glycolysis released into the blo
ID: 38962 • Letter: B
Question
Bisphosphoglyceric acid (BPG) is a byproduct of glycolysis released into the bloodstream when an animal's supply of oxygen is low. It binds with greater affinity to partially deoxygenated hemoglobin than it does oxygenated hemoglobin and decreases its affinity for O2, promoting release of remaining oxygen molecules to the sites that need it most. Considering the 4 steps of gas exchange in Fig. 39.3 of your textbook, in which stage would you expect to find BPG exhibiting its greatest affinity for hemoglobin? Circle your answer and explain.
1. Ventilation by bulk flow
2. Diffusion across respiratory surface
3. Circulation by bulk flow
4. Diffusion between blood and cells
Explanation / Answer
In diffusion across respiratory surface stage the BPG exhibits its greatest affinity for hemoglobin, this is because in low oxygen conditions it undergoes spatial arrangements or allosteric confirmation to fit into deoxyhemoglobin molecule with high affinity. The 2,3 BPG binds with greater affinity to deoxygenated hemoglobin when the red cell is near respiring tissue than it binds to oxygenated hemoglobin in the lungs. The binding of 2,3-BPG to deoxyhemoglobin, stabilizes the low oxygen affinity state (T state) of the oxygen carrier or hemoglobin. 2,3 BPG fits into the cavity of the deoxy- conformation,changing the molecular symmetry with positive polarity by the formation of salt bridges with lysine and histidine residues in the beta subunits of hemoglobin.
Therfore, the option 2 is correct.
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