Answer:

Oxygen (O2) COMPETITIVELY and reversibly binds to hemoglobin, with certain changes within the environment altering the affinity in which this relationship occurs. The sigmoidal shape of the oxygen dissociation curve illustrates hemoglobin’s propensity for positive cooperativity, as hemoglobin undergoes conformational changes to increase its affinity for oxygen as molecules progressively bind to each of its four available BINDING sites. The Bohr effect describes hemoglobin’s lower affinity for oxygen secondary to increases in the partial pressure of carbon dioxide and DECREASES in blood pH. This lower affinity, in turn, enhances the unloading of oxygen into tissues to meet the oxygen demand of the tissue

Increases in PCO2 and Decreases in pH  

Through the biochemical reactions necessary for cellular respiration, increases in metabolic activity within tissues result in the production of carbon dioxide (CO2) as a metabolic waste product. This increase in tissue PCO2 leads to an increase in hydrogen ion (H+) concentration, represented as a decrease in pH as the environment undergoes the process of acidosis. These effects decrease hemoglobin’s affinity for oxygen, weakening it’s binding capacity and increasing the likelihood of dissociation; this is represented as a rightward shift of the hemoglobin dissociation curve, as hemoglobin unloads oxygen from its binding sites at higher partial pressures of oxygen. Specifically, it is the association of protons (H+ ions) with the amino acids in hemoglobin that cause a conformational change in protein folding, ultimately reducing the affinity of the binding sites for oxygen molecules. This configuration shift of hemoglobin under the influence of protons is classified as the taut (T) form.

Hemoglobin exists in 2 forms, the taut form (T) and the relaxed form (R). This structural change to the taut form leads to low-affinity hemoglobin whereas the relaxed form leads to a high-affinity form of hemoglobin, with respect to oxygen binding. In the lungs, the highly saturated oxygen environment can overcome the lower affinity T-form of hemoglobin, effectively binding despite disadvantageous binding capacity. During this process, initial O2 binding induces an alteration in hemoglobin from the taut to relaxed form, dissociating H+ protons and progressively increasing hemoglobin’s affinity for oxygen at each of the remaining binding sites through positive cooperativity. Under the influence of acidic environments, hemoglobin has a propensity for undergoing the reverse of this conformational change, releasing oxygen in favor of the attachment of H+ protons as hemoglobin shifts from the higher oxygen affinity relaxed form to the lower oxygen affinity taut form.

Overall, this relationship can be quantified by an increase in the P50, as 50% hemoglobin oxygen saturation is achieved at higher-than-normal values of pO2, in comparison to the accepted normal P50 of 27 mmHg. This RESULTS in a greater unloading of oxygen in the presence of the acidic environments surrounding body tissues as a result of cellular respiration