16. Bohr Effect

7. Why is more oxygen unloaded from hemoglobin in an actively metabolizing tissue than in a resting tissue, even at the same concentration of O2?

At the lower pH of an actively metabolizing tissue, hemoglobin has a lower affinity for oxygen. Actively metabolizing tissue produces more CO2, which in turn leads to more H+ and a lower pH than tissue at rest. Affinity decreases at low pH, which favors the T (deoxygenated) state of hemoglobin. See "The Bohr Effect Enhances Oxygen Transport" (especially Figure 3-13 - "Carbonic Anhydrase"), in Module 3, for more information.

41. Which line on the graph represents hemoglobin's oxygen binding curve at a pH that is lower than 7.4?

A Correct!. The Bohr effect states that affinity drops as pH drops. Therefore, the curve with the lower affinity than the pH 7.4 curve is Curve A. See "The Bohr Effect Enhances Oxygen Transport" in Module 3 for more information.

34. Why is more oxygen unloaded from hemoglobin in an actively metabolizing tissue than in a resting tissue, even at the same concentration of O2?

At the lower pH of an actively metabolizing tissue, hemoglobin has a lower affinity for oxygen.

22. 2,3 BPG is a molecule that binds reversibly to hemoglobin's protein subunits and stabilizes hemoglobin in the T state. Is hemoglobin oxygenated or deoxygenated under these conditions?

Deoxygenated

36. Hemoglobin's ability to bind or release oxygen depends on the pH of the environment. This behavior is known as the Bohr effect. Considering this, which of the following statements is true?

Hemoglobin binds to oxygen at high pH and releases oxygen at low pH.

2. Which statement describes the affinity of hemoglobin for oxygen?

Hemoglobin has high affinity for oxygen in the R state and a low affinity for oxygen in the T state.

32. Which of the following is expected in the lungs? (Choose all that apply)

Hemoglobin is in the R state. The heme group is planar. The subunits are closer together than they are in the deoxygenated state.

1. Which statement describes the conformational state (shape) of hemoglobin?

Hemoglobin is in the relaxed (R) state when oxygenated and in the tense (T) state when de-oxygenated.

39. Which way will hemoglobin's oxygen-binding curve shift if a change in conditions leads hemoglobin to have an increased affinity for oxygen?

Hemoglobin's oxygen-binding curve shifts to the left and up as affinity for oxygen increases.

21. Which of the following stabilizes the R state of hemoglobin?

High O2 concentration

7. Does oxygenated hemoglobin have a high or low affinity for carbon monoxide (CO)?

High affinity for CO

1. Does oxygenated hemoglobin have a high or low affinity for carbon monoxide (CO)?

High affinity for CO Carbon monoxide (CO), which is similar in shape to oxygen (O2), binds to the iron (Fe) atom in the heme group when hemoglobin is in the R state and the heme group is planar, just like oxygen does. Hemoglobin binds to carbon monoxide with 200 times the affinity of oxygen, which means it is very difficult to get rid of the carbon monoxide once it is bound to hemoglobin. See "Carbon Monoxide Poisoning: A Problem with Hemoglobin Function" in the Module 3 text for more information.

30. Which one of the following statements is true about the following graph?

High concentration of carbon dioxide and high concentration of protons (H+) in the surrounding tissue will shift the graph to the right.

9. Is oxygenated hemoglobin favored by low pH or high pH?

High pH

23. 2,3 BPG is a molecule that binds reversibly to hemoglobin's protein subunits and stabilizes hemoglobin in the T state. What impact does this have on hemoglobin's ability to bind oxygen?

Oxygen binding ability decreases

19. Tissues at rest have an oxygen concentration of 40 Torr. Which pH corresponds to the lowest saturation of hemoglobin by oxygen?

pH 7.2

20. Tissues at rest have an oxygen concentration of 40 Torr. Which pH would result in more oxygen being delivered to the tissue?

pH 7.2

20. Tissues at rest have an oxygen concentration of 40 Torr. Which pH would result in more oxygen being delivered to the tissue?

pH 7.2 The pH that would result more oxygen being delivered to the tissue is the pH with the lowest fraction of hemoglobin with oxygen bound (=affinity). The Bohr effect says this will be the lowest pH. Hemoglobin at pH 7.2 has the lowest fraction with O2 bound (0.60 or 60%) at 40 Torr, compared to pH 7.4 (0.7 or 70%) and pH 7.6 (~0.85, or 85%).

16. Below is a picture of the hemoglobin dissociation curve at different pH levels. Which curve demonstrates the saturation of hemoglobin in the lungs?

pH 7.6

15. What happens to oxygenated hemoglobin as the amount of CO2 increases?

pH decreases, Hb shifts more to the T state, oxygen affinity decreases

2. What happens to oxygenated hemoglobin as the amount of CO2 increases?

pH decreases, Hb shifts more to the T state, oxygen affinity decreases pH decreases, Hb shifts more to the R state, oxygen affinity increases", the answer is incorrect. While pH does decrease as CO2 increases, when the CO2 combines with water to form H+ and bicarbonate, decreasing pH favors the T state and low affinity, not the R state and high affinity. See "The Bohr Effect Enhances Oxygen Transport" in Module 3 for more information.

11. What happens to oxygenated hemoglobin as the O2 concentration increases? (Select all that apply)

It tends to retain bound oxygen It picks up additional oxygen (up to 4 total) and shifts to the R state

12. What happens to deoxygenated hemoglobin as the amount of O2 (pO2) increases? (Select all that apply)

It tends to retain bound oxygen It picks up additional oxygen (up to 4 total) and shifts to the R state

5. How many oxygen molecules are bound to deoxygenated hemoglobin?

0 oxygen molecules

17. Tissues at rest have an oxygen concentration of 40 Torr. What is the fraction of hemoglobin with oxygen bound (hemoglobin saturation) at 40 torr and at pH 7.2?

0.5

3. Tissues at rest have an oxygen concentration of 40 Torr. What is the fraction of hemoglobin with oxygen bound (hemoglobin saturation) at 40 torr and at pH 7.2?

0.5

17. Tissues at rest have an oxygen concentration of 40 Torr. What is the fraction of hemoglobin with oxygen bound (hemoglobin saturation) at 40 torr and at pH 7.2?

0.5 In order to find the fraction of hemoglobin with oxygen bound at any oxygen concentration, you draw an imaginary line straight up from the number on the oxygen concentration access until you get two the line on the graph, then dropped another imaginary line straight to the left until you get to the fraction of hemoglobin with oxygen bound access. If you do this, you would come to the pH 7.2 curve first, followed by the pH 7.4 curve, and then the pH 7.6 curve. Starting at the 40 torr mark, going straight up to the FIRST curve, which is the pH 7.2 curve, and then straight to the left, you would cross the vertical axis at about 0.5, or 50%. See "The Bohr Effect Enhances Oxygen

18. Tissues at rest have an oxygen concentration of 40 Torr. What is the fraction of hemoglobin with oxygen bound (hemoglobin saturation) at 40 torr and at pH 7.6?

0.8

4. How many oxygen molecules are bound in oxygenated hemoglobin?

1 to 4 oxygen molecules

10. Due to the Bohr effect, how will the curve below shift in response to changes in pH?

An increase in H+ concentration will shift hemoglobin's oxygen-binding curve to the right, while a decrease in H+ concentration will shift the curve to the left.

40. Due to the Bohr effect, how will the curve below shift in response to changes in pH?

An increase in H+ concentration will shift hemoglobin's oxygen-binding curve to the right, while a decrease in H+ concentration will shift the curve to the left.

38. Which of the following statements is true?

As carbon dioxide (CO2) concentration in a cell increases, H+ concentration increases and pH decreases.

31. Which of the following statements are true? (Choose all that apply)

As pH decreases, hemoglobin's affinity for oxygen decreases. As 2,3-BPG decreases, hemoglobin's affinity for oxygen increases.

5. Which of the following statements are true? (Choose all that apply)

As pH decreases, hemoglobin's affinity for oxygen decreases. As 2,3-BPG decreases, hemoglobin's affinity for oxygen increases.

33. Gas exchange between maternal blood and fetal blood takes place in the placenta. If curve c in the following graph represents the dissociation curve of adult hemoglobin, which curve would represent the dissociation curve of fetal hemoglobin?

Curve b

6. Gas exchange between maternal blood and fetal blood takes place in the placenta. If curve c in the following graph represents the dissociation curve of adult hemoglobin, which curve would represent the dissociation curve of fetal hemoglobin?

Curve b

Learning Objective

Given a scenario regarding hemoglobin, the student explains how pH influences its function. (2 questions on the assessment)

37. Hemoglobin acts as a buffer and controls the pH of the blood by binding to __________.

H+ ions

9. Hemoglobin acts as a buffer and controls the pH of the blood by binding to __________.

H+ ions

6. Where does carbon monoxide (CO) bind hemoglobin?

Iron (Fe)

8. Does deoxygenated hemoglobin have a high or low affinity for carbon monoxide (CO)?

Low affinity for CO

10. Is deoxygenated hemoglobin favored by low pH or high pH?

Low pH The T state of hemoglobin is favored by low pH and induces the release of oxygen, while the R state is favored by higher pH and stimulates hemoglobin to bind more O2 by increasing its affinity for oxygen. This phenomenon is known as the Bohr effect. See "The Bohr Effect Enhances Oxygen Transport

35. Acidosis occurs as a result of cardiac arrest. Which of the following is the theoretical reason why sodium bicarbonate might be administered to your patient during a cardiac arrest?

The bicarbonate acts to increase pH, which may allow hemoglobin to transport oxygen more efficiently.

23. 2,3 BPG is a molecule that binds reversibly to hemoglobin's protein subunits and stabilizes hemoglobin in the T state. What impact does this have on hemoglobin's ability to bind oxygen?

Oxygen binding ability decreases 2,3-BPG is secreted by the red blood cells of pregnant mothers and those who live at high altitudes. In both cases, hemoglobin needs to be especially efficient at delivering its oxygen, to a developing fetus in the case of the pregnant mother, and to the tissues in the case of those who live at high altitude where oxygen is relatively scarce. Stabilizing the T state of hemoglobin, which has low oxygen affinity and decreased oxygen binding ability, ensures more efficient release of oxygen. See "The T-State is Favored by 2,3-BPG" in Module 3 for more information.

26. Which statement describes the relationship between the pH in the lungs and peripheral tissues?

Relative to the lungs, the pH in the peripheral tissues is lower because the CO2 generated by metabolism is converted to bicarbonate, which releases protons (H+).

4. Which statement describes the relationship between the pH in the lungs and peripheral tissues?

Relative to the lungs, the pH in the peripheral tissues is lower because the CO2 generated by metabolism is converted to bicarbonate, which releases protons (H+).

14. What happens to Deoxygenated Hemoglobin as the amount of H+ decreases?

Shifts more to the R state, picks up additional oxygen (if possible)

13. What happens to oxygenated hemoglobin as the amount of H+ decreases?

Shifts more to the R state, picks up additional oxygen (if possible) As H+ decreases, pH increases and the R state is increasingly favored. Hemoglobin in the R state has a high affinity for oxygen and will bind up to four oxygen molecules in a cooperative way. See Figure 3-11 ("Cooperativity of hemoglobin)"

14. What happens to Deoxygenated Hemoglobin as the amount of H+ decreases?

Shifts more to the R state, picks up additional oxygen (if possible) As H+ decreases, pH increases and the R state is increasingly favored. Hemoglobin in the R state has a high affinity for oxygen and will bind up to four oxygen molecules in a cooperative way. See Figure 3-11 ("Cooperativity of hemoglobin)"

29. Which one of the following statements is true about the graph shown below?

The T state of hemoglobin is favored by low pH and induces the release of oxygen.

8. Acidosis occurs as a result of cardiac arrest. Which of the following is the theoretical reason why sodium bicarbonate might be administered to your patient during a cardiac arrest?

The bicarbonate acts to increase pH, which may allow hemoglobin to transport oxygen more efficiently. "The bicarbonate acts to increase pH, prompting hemoglobin to shift to the R state and pick up CO2 that has accumulated during the cardiac arrest", the answer is incorrect. While solutions of a bicarbonate salt (e.g. baking soda) increase the pH of the body by binding to protons (H+) to form CO2 and water, protons (H)+, not CO2, bind to the hemoglobin. See "The Bohr Effect Enhances Oxygen Transport" (especially Figure 3-13 - "Carbonic Anhydrase"), in Module 3, for more information. 9. Hemoglobin acts as a buffer and controls the

3. Which statement describes the shape of the heme group in hemoglobin?

The heme group is bent when not bound to oxygen and planar when bound to oxygen.

28. Which one of the following statements is true about the graph shown below?

The oxygen binding curve shifts to the right when the pH of the surrounding tissue is low and the majority of the hemoglobin is in the T state.

25. The Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the pH of the surroundings. Which of the following statements describes hemoglobin at HIGH pH?

When the pH is high, hemoglobin has a high affinity for oxygen and binds oxygen.

24. The Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the pH of the surroundings. Which of the following statements describes hemoglobin at LOW pH?

When the pH is low, hemoglobin has low affinity for oxygen and releases oxygen.

27. The Bohr effect is a relationship between hemoglobin's oxygen binding behavior in conjunction with the pH of the surroundings. When the H+ ion concentration increases, the pH of the solution _________________.

decreases when pH decreases H+ concentration increases, and vice versa. Oxygen concentration has no direct effect on pH. However, in the body, where oxygen concentration is low, CO2 concentration is high. CO2 is generated by the citric acid cycle (CAC) in tissues breaking down carbohydrates and fats for energy. The CO2 combines with water to form bicarbonate and H+ (protons) by the enzyme carbonic anhydrase. Increased H+ concentration lowers the pH