The Chloride Shift (Cambridge (CIE) AS Biology): Revision Note

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 then red blood cells would become positively charged as a result of a build up of hydrogen ions formed from the dissociation of carbonic acid