The Chloride Shift (Cambridge International A-Level Biology)

Spec point — 8.2.2 · describe the chloride shift and explain the importance of the chloride shift

The Chloride Shift

• The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogencarbonate ions are formed

• Hydrogencarbonate ions are formed by the following process:

  • Carbon dioxide diffuses into red blood cells
  • The enzyme carbonic anhydrase catalyses the combining of carbon dioxide and water to form carbonic acid (H₂CO₃)

CO₂ + H₂O ⇌ H₂CO₃

• Carbonic acid dissociates to form hydrogen carbonate ions and hydrogen ions

H₂CO₃⇌ HCO₃^-+ H⁺

• Negatively charged hydrogencarbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane

• To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein

  • If this did not occur, the loss of negative hydrogencarbonate ions would leave the inside of the red blood cell positively charged

Exam Hint Be sure to learn the differences between the Bohr shift and chloride shift. The Bohr shift occurs when a high partial pressure of carbon dioxide causes haemoglobin to release oxygen into respiring tissues, while the chloride shift refers to the movement of chloride ions into red blood cells.