890403-23

890403-23
Caption: Hemoglobin crystals. Hemoglobin or haemoglobin is the iron-containing oxygen-transport metalloprotein in the red cells of the blood in mammals and other animals. The molecule consists of globin (the apoprotein) and four heme (haem) groups (an organic molecule with an iron atom). Heme groupAt the core of the molecule is a heterocyclic ring, known as a porphyrin which holds an iron atom; this iron atom is the site of oxygen binding. An iron containing porphyrin is termed a heme. The name hemoglobin is the concatenation of heme and globin, a globin being a generic term for a globular protein. There are a number of heme containing proteins. Hemoglobin is by far the best known. In adult humans, hemoglobin is a tetramer (contains 4 subunit proteins), consisting of two alpha and two beta subunits noncovalently bound. Each subunit of hemoglobin contains a single heme, so that the overall binding capacity of adult human hemoglobin for oxygen is four oxygen molecules. The control of hemoglobin's affinity for oxygen by the binding and release of carbon dioxide is known as the Bohr effect. When red cells reach the end of their life, they are broken down, and the hemoglobin molecule broken up and the iron recycled. When the porphyrin ring is broken up, the fragments are normally secreted in the bile by the liver. Mutations in the gene for the hemoglobin protein result in a group of hereditary diseases termed the hemoglobinopathies, the most common members of which are sickle cell anemia and thalassaemia. Decreased levels of hemoglobin, with or without an absolute decrease of red blood cells, leads to symptoms of anemia. As absence of iron decreases heme synthesis, red blood cells in iron deficiency anemia are hypochromic and microcytic. Mutations in the globin chain are associated with the hemoglobinopathies, such as sickle-cell anemia and thalassemia. There is a group of genetic disorders, known as the porphyrias that are characterized by errors in metabolic pathways of heme synthesis.
Magnification*: x50
Type: LM
Copyright 1985 Dennis Kunkel Microscopy, Inc.
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