haemoglobins

Haemoglobins are protein complexes found in the red blood cells of vertebrates and many invertebrates, responsible for transporting oxygen. The most common type in humans is haemoglobin A. Each haemoglobin molecule consists of four protein chains, typically two alpha-globin chains and two beta-globin chains, surrounding a heme group. The heme group contains an iron atom that reversibly binds to oxygen molecules. In the lungs, where oxygen concentration is high, haemoglobin readily picks up oxygen. As blood circulates to tissues with lower oxygen levels, the haemoglobin releases the oxygen to meet the metabolic demands of the cells. Carbon dioxide, a waste product of metabolism, can also bind to haemoglobin, though it is primarily transported in the blood plasma. Variations in the structure of globin chains can lead to different types of haemoglobins, some of which are associated with genetic disorders like sickle cell anaemia and thalassaemia. Fetal haemoglobin, present during pregnancy, has a higher affinity for oxygen than adult haemoglobin, facilitating oxygen transfer from the mother to the fetus.