B3.1 HL Transport of Respiratory Gasses [IB Biology HL]

Overview of Gas Exchange and Hemoglobin

  • Introduction to Hemoglobin

    • Hemoglobin is a crucial protein found in red blood cells.

    • "Hemo" refers to blood, and it can transport four oxygen molecules.

Structure of Hemoglobin

  • Polypeptides and Heme Groups

    • Consists of four polypeptide chains.

    • Each polypeptide contains a heme group responsible for binding oxygen.

    • Total of four heme groups, each capable of carrying one oxygen molecule.

  • Oxygen Binding and Affinity

    • Binding of oxygen to the heme group causes a conformational change in hemoglobin.

    • This change increases hemoglobin's affinity for oxygen, allowing it to bind more effectively.

    • The binding process is reversible, so hemoglobin can release the oxygen when needed.

Oxygen Dissociation Curve

  • Definition and Importance

    • Oxygen dissociation curves represent how hemoglobin's affinity for oxygen changes with partial pressure of oxygen.

    • "Dissociate" means to separate; the curve illustrates how easily hemoglobin releases oxygen.

  • Partial Pressure Concept

    • Partial pressure refers to the pressure exerted by one gas in a mixture of gases, affecting hemoglobin's function.

    • The air we breathe is a mixture, with oxygen being a critical component affecting hemoglobin's function.

  • Adult Hemoglobin Characteristics

    • At low partial pressures, hemoglobin releases oxygen to surrounding tissues.

    • Affinity for oxygen is low in low oxygen environments.

    • At high partial pressures, hemoglobin is fully saturated with oxygen.

    • The curve is sigmoidal, indicating varying saturation levels with changing oxygen pressures.

Fetal Hemoglobin

  • Affinity for Oxygen

    • Fetal hemoglobin has a higher affinity for oxygen compared to adult hemoglobin.

    • This characteristic allows it to 'steal' oxygen from the mother's blood efficiently.

    • The oxygen dissociation curve for fetal hemoglobin shifts to the left, indicating higher saturation at the same partial pressure compared to maternal hemoglobin.

Influence of Carbon Dioxide

  • Carbon Dioxide and Affinity Changes

    • High levels of carbon dioxide can lower the pH of the environment, leading to acidosis.

    • Increased carbon dioxide levels convert hemoglobin into carbaminohemoglobin, which has a lower affinity for oxygen.

    • This results in the Bohr shift, where the oxygen dissociation curve shifts to the right, facilitating oxygen release in high CO2 environments.

Summary of Key Concepts

  • Understanding the Curves

    • When analyzing the oxygen dissociation curves:

      • Adult Hemoglobin: Shows a typical sigmoidal curve, indicating varying affinities based on oxygen pressure.

      • Bohr Shift: In high CO2, the curve shifts to the right, showing decreased affinity for oxygen.

      • Fetal Hemoglobin: The curve shifts to the left, indicating increased oxygen-binding capacity.

  • Conclusion

    • The function of hemoglobin is adapted to meet oxygen demands in various environments.

    • Hemoglobin must efficiently release oxygen where needed and effectively capture oxygen from maternal blood in the case of a fetus.