Question

Which of the following statement(s) is/are TRUE regarding the binding of oxygen to hemoglobin?

A.

The pH difference between the lungs and the surrounding tissues that decreases efficiency in oxygen transport is known as the Bohr effect.

B.

100% of CO2 is transported by formation of a carbamate bond with the amino terminal residues in the hemoglobin chains.

C.

2,3-Bisphosphoglycerate stabilizes the T state.

D.

All of the statements are true.

Answer 1

The Bohr effect is a physiological phenomenon first described by Christian Bohr stating that haemoglobin's oxygen binding affinity is inversely related both to acidity and to the concentration of carbon dioxide i.e., the Bohr effect refers to the shift in the oxygen dissociation curve caused by changes in the concentration of carbon dioxide or the pH of environment. The Bohr effect increases the efficiency of oxygen transportation through the blood. After haemoglobin binds to the oxygen in lungs due to the high oxygen concentrations, the Bohr effect facilitates its release in the tissues, particularly those tissues in most need of oxygen. The Bohr effect enables the body to adapt to changing conditions and makes it possible to supply extra oxygen to tissues that need it the most.

When carbon dioxide binds to haemoglobin, carbaminohaemoglobin is formed, lowering haemoglobin's affinity for oxygen via the Bohr effect. In absence of oxygen, unbound haemoglobin molecules have a greater chance of becoming carbaminohaemoglobin. The Haldane effect relates to the increased affinity of de-oxygenated haemoglobin for proton : offloading of oxygen to the tissues thus results in increased affinity of the haemoglobin for carbon dioxide, and proton which the body wants to get rid of, which can then be transported to the lungs for removal. Haemoglobin can bind with 4 molecules of carbon dioxide. The carbon dioxide molecules form a carbamate with the four terminal amine groups of the four protein chains in the deoxy form of the molecule. Thus, one haemoglobin can transport 4 carbon dioxide molecules back to the lungs. 23% of carbon dioxide is carried in blood in this way.

By itself, haemoglobin has sigmoid-like kinetics. In selectively binding to deoxyhaemoglobin, 2,3-Bisphosphoglycerate stabilizes the T state conformation, making it harder for oxygen to bind haemoglobin and more likely to be released to adjacent tissues.

Therefore, from above information the statement (C) is true regarding the binding of oxygen to haemoglobin.