Describe the Bohr shift and explain the importance of the Bohr shift

Sourav PanOctober 30, 2024

Answered

The Bohr shift (or Bohr effect) refers to a physiological phenomenon where hemoglobin’s affinity for oxygen decreases in response to increases in carbon dioxide (CO₂) concentration, hydrogen ion concentration (lower pH), or temperature. These changes shift the oxygen dissociation curve to the right, allowing hemoglobin to release oxygen more readily in tissues that need it most.

1. Mechanism of the Bohr Shift

• Increased CO₂ and Lower pH: In actively respiring tissues, CO₂ levels are high due to cellular respiration. CO₂ combines with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions (H⁺). This release of H⁺ lowers the pH (makes the environment more acidic).
• Effect on Hemoglobin: The increase in H⁺ ions and CO₂ causes conformational changes in hemoglobin that decrease its affinity for oxygen. Essentially, hemoglobin is less likely to hold onto oxygen in acidic or high-CO₂ environments, which is precisely where oxygen is needed.
• Rightward Shift: The decrease in oxygen affinity means hemoglobin will release more oxygen at a given partial pressure of oxygen (pO₂), which is visually represented by a rightward shift in the oxygen dissociation curve.

2. Importance of the Bohr Shift

• Enhanced Oxygen Delivery to Active Tissues: In metabolically active tissues (like muscles during exercise), increased CO₂ production, lower pH, and elevated temperatures signal that these tissues require more oxygen for energy. The Bohr shift allows hemoglobin to release more oxygen into these tissues, where it can be used in aerobic respiration to produce ATP.
• Efficient Oxygen Loading and Unloading: The Bohr effect is specifically beneficial because it occurs primarily in tissues, while hemoglobin still maintains a high affinity for oxygen in the lungs where CO₂ and H⁺ concentrations are lower. This enables efficient loading of oxygen in the lungs and unloading in tissues.
• Adaptation to Variable Metabolic Demands: The Bohr shift allows hemoglobin to adapt its oxygen delivery in response to the metabolic demands of different tissues. For example, during exercise, muscle tissues produce more CO₂ and H⁺, prompting hemoglobin to release more oxygen compared to when at rest.
• Support for Acid-Base Balance: The binding and release of H⁺ ions by hemoglobin also help maintain acid-base balance in the blood. When hemoglobin binds to H⁺ (forming haemoglobinic acid), it buffers blood pH, preventing drastic changes in acidity.