Lecture Notes: Hemoglobin and Oxygen Dissociation Curve

Introduction to Hemoglobin

• Globular Protein: Hemoglobin is a globular, water-soluble protein.
• Quaternary Structure: Composed of four polypeptide chains: 2 alpha and 2 beta globins.
• Heme Group: Each polypeptide has a heme group containing iron, which binds oxygen.

Function of Hemoglobin

• Oxygen Binding: Each hemoglobin molecule can bind 4 oxygen molecules due to its 4 heme groups, forming oxyhemoglobin (HbO₈).
• Color: Red blood cells are red due to iron-oxygen binding forming iron oxide.

Duality of Hemoglobin

• Affinity for Oxygen: High affinity for oxygen allows it to bind easily.
• Release of Oxygen: Readily releases oxygen when necessary, showing duality—attraction and willingness to release.

Oxygen Dissociation Curve

• Definition: Represents oxygen binding and release from hemoglobin in terms of partial pressures and saturation.
• Axes:
  • Y-axis: Percentage saturation of hemoglobin with oxygen.
  • X-axis: Partial pressure of oxygen (kPa).
• Curve Shape: Sigmoid or S-shaped.

Partial Pressure of Oxygen

• Concept: Reflects concentration of oxygen in an area.
• Terminology: Use "partial pressure" for gases, "concentration" for solutions.

Percentage Saturation of Oxygen in Hemoglobin

• Explanation: Ratio of current oxygen bound to total capacity.
• Examples:
  • 50% Saturation: For a hemoglobin setup with 5 molecules, if carrying 10 oxygen, then it's at 50% saturation.
  • 100% Saturation: Carrying max oxygen (e.g., 20 in the example) indicates full saturation.

Effects on the Dissociation Curve

• Low vs High Partial Pressure:
  • Low Partial Pressure: Low oxygen saturation as less oxygen is available.
  • High Partial Pressure: High saturation; hemoglobin is fully loaded with oxygen.
• Graph Interpretation:
  • Low pressure (e.g., 2 kPa) correlates with low saturation (~10%).
  • High pressure (e.g., 12 kPa) leads to high saturation (100%).

Oxygen Distribution to Cells

• Hemoglobin Release: Releases more oxygen at lower partial pressures to meet cell needs.
• Interaction with Body Cells:
  • High Oxygen Cells: Less oxygen released.
  • Low Oxygen Cells: More oxygen released.

Summary

• Hemoglobin's dual ability to bind and release oxygen is crucial for effective oxygen delivery.
• Understanding the oxygen dissociation curve helps explain how oxygen is distributed depending on environmental conditions.

Next Steps

• Upcoming Topic: How hemoglobin senses oxygen needs of cells and adjusts its oxygen release accordingly.