How does the quaternary structure of hemoglobin facilitate oxygen transport compared to myoglobin?

The quaternary structure of hemoglobin, which consists of four subunits, allows for cooperative binding of oxygen, resulting in a sigmoidal oxygen saturation curve. This means that hemoglobin can efficiently pick up oxygen in the lungs and release it in tissues where it is needed, unlike myoglobin, which has a hyperbolic curve and binds oxygen more tightly, making it less effective for transport.

Hemoglobin's quaternary structure enables cooperative binding, where the binding of oxygen to one subunit increases the likelihood of oxygen binding to the remaining subunits. This results in a sigmoidal curve for oxygen saturation, indicating that hemoglobin is more efficient at loading oxygen in high concentrations (like in the lungs) and unloading it in low concentrations (like in tissues). In contrast, myoglobin, with its single polypeptide chain, binds oxygen more tightly but does not exhibit cooperative binding, making it less effective for transporting oxygen compared to hemoglobin.