CO2 Transport

Question 1

CO2 movement

Answer 1

Moves through tissues by simple diffusion (high to low concentration)

Question 2

Three forms that CO2 exists

Answer 2

1. Dissolved in solution (CO2 is highly soluble)
2. Reversible reactions in plasma
   - Combine with terminal amino groups in plasma proteins
3. Reversible reactions in RBCs
   - Combine with terminal amino groups in hemoglobin
   - Catalyzed by carbonic anhydrase, more efficient

Question 3

Reversible reaction with CO2 (Carbonic acid equilibrium)

Answer 3

CO2 + H2O <–> H2CO3 <–> H+ + HCO3-

Question 4

Steps of CO2 transport in a RBC

Answer 4

1. Hemoglobin is deoxygenated in venous blood. Will want to be protonated.
2. CO2 diffuses freely into RBC, made into carbonic acid by carbonic anhydrase, and then further made into Hydrogen and bicarbonate
3. Chloride shift: RBCs utilize Cl anion transport pumps to exchange bicarbonate for Cl-
   - Allows more bicarbonate to be transported
4. H+ ions are trapped intracellularly and can protonate the hemoglobin

Question 5

Haldane Effect

Answer 5

Describes hemoglobins impact on CO2 transport in RBCs

Histidine coordinates O2 binding to Fe2+ (can be protonated and unprotonated)
- O2 binding leads to histidine deprotonation
- O2 unbinding results in histidine protonation

Question 6

Where would you expect to see oxygenated hemoglobin able to donate protons?

Answer 6

In arterial blood

Question 7

Where would you expect to see deoxygenated hemoglobin unable to donate protons?

Answer 7

Venous blood

Question 8

Gas exchange at tissues and CO2 transport

Answer 8

• Low O2, causes a shift to the right of equilibrium forming H2CO3 which provides HCO3- and H+ proton for giving hemoglobin a proton, favouring CO2 into RBC
• Release of O2

Question 9

Gas exchange at lungs and CO2 transport

Answer 9

• High O2, causes a shift to left forming CO2 which requires hemoglobin giving up a proton. Favouring CO2 leaving the RBC
• Gain O2