Hemoglobin: Difference between revisions

A porphyrin, known as a heterocyclic ring, locates at the core of the molecule and holds an iron atom, which is the site of oxygen binding. An iron containing porphyrin is called a heme. It is also known as the prosthetic group of hemoglobin, myoglobin, and the cytochromes. <ref> [http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb2/part1/heme.htm Synthesis of Heme] Joyce J. Diwan. Biochemistry of Metabolism </ref> Globin is the protein that protects the heme molecule. It is called a globular protein. A single unit of hemoglobin consists of a heme imbedded in a globular protein. <ref name=bioche> [http://themedicalbiochemistrypage.org/hemoglobin-myoglobin.html Hemoglobin and Myoglobin ] Michael W. King. The Medical Biochemistry Page </ref> Hemoglobin synthesis requires the coordination of heme and globin. In the mitochondria and the cytosol of immature red blood cells, the heme part is synthesized in a series of steps. On the other hand, the globin protein parts are synthesized by ribosomes in the cytosol. From the proerythroblast to the reticulocyte in the bone marrow, the production of hemoglobin continues in the cell. Then the nucleus disappears in mammalian red blood cells in only humans not in other species. Although the nucleus is lost in red blood cells, residual ribosomal RNA keeps synthesizing hemoglobin until reticulocyte loses its RNA as soon as it enters the vasculature.  

In adult humans, hemoglobin is a tetramer, which has two alpha and two beta subunits. The subunits are structurally same and have equal size. Each subunit has a molecular weight of 16,000 and a total molecular weight is about 64,000. Since each subunit of hemoglobin includes a single heme, adult human hemoglobin can hold four oxygen molecules for the total binding capacity. <ref name=bioche/>

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