Question

104 Homework 6 4. (15 points): Hemoglobin (Hb) is the main oxygen transport protein in the blood. Each hemoglobin molecule can transport four oxygen atoms at a time, one at each of its four iron-based binding sites. The binding of O2 to hemoglobin is a pH-dependent equilibrium, simplified as: Use Le Chatelier's Principle to answer the following questions: a) What form of hemoglobin, HbH" or Hb(Ojle, would be favored in the lungs? What form would be favored in the cells to which oxygen is transported? Explain in 2-4 sentences. When a person hyperventilates, the Co, concentration in the blood is decreased. thi b) How would is affect the oxygen-binding equilibrium of hemoglobin? How does breathing into a paper bag help to counteract the effects of hyperventilation? Explain. (Hint: remember the relationship between CO2 concentration and pH from Problem 3!) When a person suffers a cardiac arrest, CO2 can build up in the blood. Patients in this situation are sometimes given an injection of sodium bicarbonate (NaHCO;) solution. What is the rationale behind this treatment? Explain. c)

Answer 1

Le Chatlier's principle states that a system in equilibrium, when disturbed, alters the rates of its forward or backward reactions to effectively negate the external perturbation applied and establishes a new equilibrium now with different equilibrium concentrations.

The pH of blood is maintained by the carbonic acid-carbonate buffer. When one inhales, the carbon dioxide is converted into carbonic acid on reaction with water by an enzyme carbonic anhydrase, in the lungs.

(a) The increased concentration of oxygen in the lungs causes the equilibrium to shift to the right, favoring the formation of Hb(O₂)₄. This way, the incoming oxygen atoms enable the hemoglobin to bind to them with a greater affinity, enabling the protein transport the oxygen to other cells.

In the cells that require oxygen, the concentration of oxygen is low, causing the equilibrium to favor the formation of HbH₄⁴⁺ by releasing oxygen.

(b) When a person hyperventilates, the concentration of carbon dioxide in the lungs decreases. This causes a decrease in the concentration of carbonic acid thereby decreasing the concentration of protons in the blood. This decrease shifts the equilibrium to the left, forcing the system to conserve protons by binding it to hemoglobin, favoring the formation of HbH₄⁴⁺. So, the release of oxygen occurs excessively.

Upon breathing into a paper bag, the confined space helps conserve the carbon dioxide from exhalations resulting in the exhaled carbon dioxide to be breathed in. This then increases carbon dioxide concentration to normal levels, preventing asphyxiation.

(c) When carbon dioxide builds up in the blood, the concentration of protons increases drastically causing hemoglobin to bind to oxygen more tightly than necessary. While this is favorable in the lungs, such increased affinity outside the lungs prevent the cells from getting the oxygen they require.

When sodium bicarbonate is added, the salt forms a buffer system with the excess carbonic acid formed, thus decreasing the proton concentration by common ion effect. After the acidity is reset to normal levels, the equilibrium shifting to the right is favored again, now by a decreased proton concentration driving oxygen binding.