Hemoglobin is a conjugated iron containing a metalloprotein with four heme molecules linked to the protein portion called “globin.” Globin part consists of 4 polypeptide chains. Normal hemoglobin consists of 2 alpha and 2 beta chains. Oxygen is bound to the ferrous (Fe2+) atoms of the haem to form oxyhemoglobin. Myoglobin is a monomeric protein of red muscle, stores oxygen as a reserve against oxygen deprivation. It releases oxygen during severe exercise for use in muscle mitochondria for aerobic synthesis of ATP. The oxygen binding curve for hemoglobin is sigmoidal in shape but myoglobin is hyperbolic. Defect in the synthesis of hemoglobin results in the formation abnormal hemoglobin (sickle cell hemoglobin). The reduction in the globin chain synthesis results in thalassemia. Hemoglobin can be differentiated by electrophoresis. Heme synthesis takes place in mitochondrion and cytosol which depends on succinyl CoA, glycine, ALA synthase and iron. Catabolism of heme results in bilirubin.