The Chloride Shift (CIE A Level Biology)

• The chloride shift is the movement of chloride ions into red blood cells that occurs when hydrogen carbonate ions are formed
• Hydrogen carbonate 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 buildup of hydrogen ions formed from the dissociation of carbonic acid