The Bohr Effect and Oxygen Dissociation Curve

Key Concepts

• Bohr Effect: Describes how the affinity of hemoglobin for oxygen changes in different parts of the body.
• Oxygen Dissociation Curve: Graph showing the relationship between the partial pressure of oxygen (pO2) and the percentage saturation of hemoglobin with oxygen.

Oxygen Dissociation Curve

• X-axis: Partial pressure of oxygen (pO2) in kilopascals (kPa)
• Y-axis: Percentage saturation of hemoglobin with oxygen

Observations

• High pO2 (Lungs): High saturation (~98%)
• Low pO2 (Respiring Tissues): Lower saturation (~36%)

Mechanism of Oxygen Binding and Release

• Reversible Reaction
  • Hemoglobin (Hb) + Oxygen (O2) <=> Oxyhemoglobin (HbO2)
  • Lungs: High pO2 shifts equilibrium to the right, favoring oxyhemoglobin.
  • Respiring Tissues: Low pO2 shifts equilibrium to the left, releasing oxygen.

Le Chatelier's Principle

• High concentration of reactants favors the forward reaction.
• Low concentration of reactants favors the reverse reaction.

Cooperative Binding

• Hemoglobin has 4 polypeptide chains, each able to bind an O2 molecule.
• One molecule released: Alters configuration, making it easier to release the next molecule.
• One molecule binds: Makes it easier for subsequent molecules to bind.
• Results in the steep S-shaped curve of the dissociation graph.

Effect of Carbon Dioxide

• Normal CO2 Levels: Standard dissociation curve
• High CO2 Levels (Respiring Tissues): Curve shifts right, lower oxygen affinity
  • Example: At pO2 of 5 kPa, saturation drops from ~70% to ~40%
• Low CO2 Levels (Lungs): Curve shifts left, higher oxygen affinity
  • Example: At pO2 of 7 kPa, saturation increases from ~90% to a higher value

The Bohr Effect

• Describes the rightward shift in the dissociation curve in response to increased CO2.
• Higher CO2 levels result in decreased oxygen affinity of hemoglobin.
• Facilitates oxygen release in respiring tissues where it is needed.

Summary

• The Bohr Effect enhances oxygen unloading in tissues with high CO2 concentration and enhances oxygen loading in the lungs with low CO2 concentration.
• Essential for efficient oxygen transport and release in the body.

Important Terminology

• pO2: Partial pressure of oxygen
• Affinity: The binding strength between hemoglobin and oxygen