The Bohr Shift Is How Carbon Dioxide Drives Oxygen Release in Respiring Tissues
Definition
Bohr Shift
- The Bohr shift (or Bohr effect) describes how haemoglobin’s affinity for oxygen decreases in the presence of high levels of carbon dioxide (CO₂) or in acidic environments (lower pH).
- The Bohr Effect describes how increased carbon dioxide levels and lower pH in active tissues reduce haemoglobin’s affinity for oxygen, promoting oxygen release.
- This adaptation ensures that oxygen delivery increases in tissues where it’s needed the most, such as during aerobic respiration.
How the Bohr Shift Works
1. Carbon Dioxide and pH Reduction
- Reaction in Red Blood Cells: $$ \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}^+ + \text{HCO}_3^- $$
- Carbon dioxide combines with water, forming hydrogen ions (H⁺) and hydrogen carbonate ions (HCO₃⁻).
- The H⁺ ions lower the blood’s pH (making it more acidic), which reduces haemoglobin’s affinity for oxygen.
- In active muscles, where carbon dioxide concentration is high, the pH drops to around 7.2.
- In the lungs, where carbon dioxide levels are low, the pH is closer to 7.4, promoting oxygen binding to haemoglobin.
2. Formation of Carbaminohaemoglobin
- Reaction with Haemoglobin:$$ \text{Haemoglobin} + 4\text{CO}_2 \\
\leftrightarrow \text{Carbaminohaemoglobin} $$ - Each haemoglobin molecule can reversibly bind carbon dioxide at the amino terminals of its polypeptides, forming carbaminohaemoglobin.
- This modification lowers haemoglobin’s oxygen affinity, promoting oxygen release in respiring tissues.
Carbaminohaemoglobin can transport four molecules of carbon dioxide back to the lungs, where it dissociates to allow carbon dioxide removal.
Why is the Bohr Effect Important?
- Oxygen Delivery to Tissues: In active tissues with high carbon dioxide production, the Bohr Effect ensures oxygen is readily released to support aerobic respiration.
- Efficient Gas Exchange in the Lungs: In the lungs, low carbon dioxide levels allow haemoglobin to regain its high affinity for oxygen, ensuring it becomes fully saturated before traveling to the tissues.
Without the Bohr Effect, tissues under high metabolic demand would struggle to receive adequate oxygen for respiration.
Self review- How does an increase in CO(_2) concentration lead to greater oxygen release from haemoglobin?
- Why does the Bohr shift not interfere with oxygen loading in the lungs?
- How does the Bohr shift support aerobic respiration in active tissues?
