Why does the rise in temperature decrease affinity of hemoglobin for oxygen?

The rise in temperature decreases the affinity of hemoglobin for oxygen due to several factors:

1. Increased Kinetic Energy: As temperature increases, the kinetic energy of molecules increases. This leads to increased molecular motion and collisions, including collisions between hemoglobin and oxygen molecules. The increased kinetic energy makes it more difficult for oxygen to bind to hemoglobin, reducing the affinity of hemoglobin for oxygen.

2. Protein Structural Changes: Hemoglobin is a protein, and its structure is affected by temperature. At higher temperatures, the protein structure of hemoglobin undergoes conformational changes. These changes can disrupt the binding site for oxygen, making it less complementary to the oxygen molecule and reducing the affinity of hemoglobin for oxygen.

3. Allosteric Effects: Hemoglobin exhibits cooperative binding behavior due to its allosteric properties. The binding of oxygen to one subunit of hemoglobin affects the affinity of the other subunits for oxygen. At higher temperatures, the cooperative effects are diminished, and the affinity of hemoglobin for oxygen decreases.

4. Bohr Effect: The Bohr effect states that the affinity of hemoglobin for oxygen is decreased by the presence of protons (H+) and carbon dioxide (CO2). As temperature increases, the solubility of CO2 in blood decreases, causing a release of CO2 from hemoglobin. This leads to a decrease in the Bohr effect, resulting in a reduced affinity of hemoglobin for oxygen.

5. Altered Hydrophobic Interactions: Hydrophobic interactions play a role in the binding of oxygen to hemoglobin. At higher temperatures, the hydrophobic interactions between hemoglobin and oxygen are weakened, making it easier for oxygen to dissociate from hemoglobin and reducing the affinity of hemoglobin for oxygen.

These factors collectively contribute to the decrease in affinity of hemoglobin for oxygen as temperature rises. This temperature dependence of hemoglobin's oxygen affinity is important in physiological processes, such as the release of oxygen from hemoglobin in tissues where the temperature is slightly higher.