provides a comprehensive look at the
who, what, when and how of Hemoglobin
Hemoglobin definition - medical term
The oxygen-carrying pigment and predominant protein in the
red blood cells. Hemoglobin forms an unstable, reversible bond with oxygen. In its
oxygenated state it is called oxyhemoglobin and is bright red. In the reduced state
it is called deoxyhemoglobin and is purple-blue.
Each hemoglobin molecule is made up of four heme groups surrounding a globin
group. Heme contains iron and gives a red color to the molecule. Globin consists
of two linked pairs of polypeptide chains. The development of each chain is controlled
at a separate genetic locus. Changes in the amino acid sequence of these chains
results in abnormal hemoglobins. For example, hemoglobin S is found in sickle-cell
disease, a severe type of anemia in which the red cells become sickle-shaped when
oxygen is in short supply.
When red blood cells die, the hemoglobin within them is released and broken up:
the iron in hemoglobin is salvaged, transported to the bone marrow by a protein
called transferrin and used again in the production of new red blood cells; the
remainder of the hemoglobin becomes a chemical called bilirubin that is excreted
into the bile which is secreted into the intestine, where it gives the feces their
characteristic yellow-brown color.
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