Hemoglobin and Its Function

Overview

• Hemoglobin is composed of globin proteins and heme (iron-rich compound).
• Found in red blood cells (RBCs), involved in oxygen transport.

Structure of Hemoglobin

• Lack of Nucleus in RBCs:
  • Increases space for hemoglobin.
• Hemoglobin Molecules per RBC:
  • Approximately 300 million.
• Quaternary Structure:
  • Composed of four globin subunits (common configuration: 2 alpha and 2 beta).
  • Each subunit contains a heme group for oxygen binding.

Oxygen Binding

• Each hemoglobin molecule can bind up to four oxygen molecules (one per heme group).
• Location of Binding:
  • Occurs in the lungs where oxygen concentration is high.
• Cooperative Binding:
  • Binding of one oxygen molecule induces conformational changes, making it easier for additional oxygen molecules to bind.

Oxygen Dissociation Curve

• Graph Characteristics:
  • X-axis: Partial pressure of oxygen (measure of oxygen concentration).
  • Y-axis: Percentage saturation of hemoglobin.
  • The curve is sigmoidal (S-shaped).

Oxygen Transport and Release

• Hemoglobin transports oxygen to tissues and unloads it into cells needing oxygen for respiration.
• Effect of Carbon Dioxide (CO2):
  • CO2 creates an acidic environment in tissues, lowering the affinity of hemoglobin for oxygen.
  • Small decrease in pH leads to a large decrease in oxygen saturation.
• Bohr Effect:
  • Increased CO2 levels (e.g., after exercise) shift the curve to the right, facilitating oxygen release.

Fetal Hemoglobin

• Fetal hemoglobin differs from adult hemoglobin (2 alpha and 2 gamma chains).
• Higher affinity for oxygen enables effective oxygen uptake from maternal hemoglobin.

Variability in Hemoglobin

• Hemoglobin types vary across organisms, influencing their oxygen dissociation curves.
• Example - Animals at High Altitudes:
  • Have hemoglobin that shifts the dissociation curve to the left to capture oxygen more efficiently in low oxygen environments.