O2 Dissociation Curve

• Oxygen dissociation curves show the affinity of haemoglobin for oxygen
• Haemoglobin is composed of four polypeptide chains, each with an iron-containing heme group that reversibly binds oxygen
• Each haemoglobin can reversibly bind up to four oxygen molecules (Hb + 4O2 = HbO8)
• As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
• Haemoglobin will have a higher affinity for O2 in oxygen-rich areas (like the lung), promoting oxygen loading
• Haemoglobin will have a lower affinity for O2 in oxygen-starved areas (like muscles), promoting oxygen unloading
• The oxygen dissociation curve for adult haemoglobin is sigmoidal (S-shaped) due to cooperative binding
• Fetal hemoglobin has a higher affinity for oxygen than adult hemoglobin
• Fetal hemoglobin's dissociation curve is shifted to the left
• Fetal hemoglobin will load oxygen when adult hemoglobin is unloading it, such as in the placenta
• Myoglobin is an oxygen-binding molecule found in skeletal muscle tissue
• Myoglobin is made of a single polypeptide with only one heme group and is not capable of cooperative binding
• The oxygen dissociation curve for myoglobin is logarithmic
• Myoglobin has a higher affinity for oxygen than adult hemoglobin and becomes saturated at lower oxygen levels
• Myoglobin will hold onto its oxygen supply until levels in the muscles are very low, helping to slow the onset of anaerobic respiration and lactic acid formation during exercise