What chemical is responsible for binding carbon dioxide to hemoglobin?
A Amylase
B Surfactant
C Oxyhemoglobin
D Carbaminohemoglobin
E Plasma Albumins
The correct answer and explanation is:
The correct answer is D. Carbaminohemoglobin.
Hemoglobin in red blood cells has the primary role of transporting oxygen from the lungs to tissues and returning carbon dioxide (CO₂) from tissues to the lungs. Hemoglobin can bind to CO₂ to form a compound called carbaminohemoglobin. This binding occurs when CO₂ interacts with the amino groups of the hemoglobin molecule.
Carbaminohemoglobin accounts for about 20-30% of the CO₂ transported in the blood. The remaining CO₂ is transported either dissolved in plasma or as bicarbonate ions, which form through the action of the enzyme carbonic anhydrase. This enzyme helps convert CO₂ into carbonic acid, which then dissociates into bicarbonate and hydrogen ions.
The binding of CO₂ to hemoglobin differs from the binding of oxygen, which binds to the iron atom in the heme group of hemoglobin. CO₂ binding, however, occurs at different sites in the hemoglobin molecule, primarily at the amino groups of the polypeptide chains. The formation of carbaminohemoglobin helps to facilitate the release of oxygen in tissues because the binding of CO₂ to hemoglobin promotes the unloading of oxygen. This is part of the Bohr effect, where the presence of high CO₂ concentrations in tissues causes hemoglobin to release oxygen more readily.
Once carbaminohemoglobin reaches the lungs, the CO₂ is released from hemoglobin and exhaled. This release is promoted by the lower concentration of CO₂ in the lungs, which shifts the equilibrium and causes CO₂ to dissociate from hemoglobin, completing the cycle of gas exchange.
Understanding how CO₂ binds to hemoglobin and the role of carbaminohemoglobin is crucial in explaining how blood transports both oxygen and carbon dioxide effectively.