Hemoglobin

Hemoglobin is an oxygen-carrying protein, and acts as such in most mammals (Friedman 1273). Typically, hemoglobins have a tetrameric structure consisting of two ? polypeptide chains of 141 amino acids each and two ? polypeptide chains of 146 amino acids each, with each subunit containing an iron-porphyrin (heme) oxygen-binding site (Friedman 1273). Each polypeptide chain forms a ball around a heme group (Hardison 128). Hemoglobin is a very abundant protein in mammals, and gives red blood cells their color when it binds oxygen (Hardison 128). Hemoglobin binds oxygen in the lungs and transports it to tissues in the body which require it for respiration (Hardison 128). An oxygen carrier is needed because oxygen is not sufficiently soluble in plasma to supply the needs of the tissues of the body (Devlin 1026). If one was not present, the blood would have to circulate 87 times as fast as it does to supply the oxygen needs of the body (Devlin 1026).

Hemoglobin A is the major hemoglobin found in adult humans, comprising about 90 percent of their total hemoglobin (Devlin 1030). Two to three percent of adult hemoglobin is hemoglobin A2, which has two ? chains and two ? chains, which differ in amino acid sequence to ? chains and are under independent genetic control (Devlin 1030). There are several modified version of hemoglobin A in the human, most with sugars such as glucose, glucose-6-phosphate or fructose 1,6-bisphosphate bound to them. The most significant is hemoglob

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: the high levels of oxygen in the lungs encourages the release of carbon dioxide and oxygen uptake, while the reverse is true in the tissues (Devlin 1026). Hemoglobin has a short lifespan in plasma, rapidly dissociating into ?? dimers, which are bound by a plasma protein known as haptoglobin and removed from the circulation (Devlin 1026). Hemoglobin within erythrocytes has a lifespan of approximately 120 days - the lifespan of an erythrocyte (Berkow, Beers and Fletcher 746). Abnormal forms of hemoglobin in humans cause anemia because they cannot carry sufficient oxygen to the tissues, and diseases such as sickle cell anemia, hemoglobin C disease, hemoglobin S-C (a combination of sickle cell disease and hemoglobin C disease) and hemoglobin E disease(Berkow, Beers and Fletcher 751). These disease are found primarily in Blacks. and hemoglobin E disease is also found in some Southeast Asians (Berkow, Beers and Fletcher 751). These hemoglobinopathies may involve the substitution of an amino acid in one of the polypeptide chains, or may be caused by an omission of an amino acid from a polypeptide chain of the hemoglobin (Devlin 1030). Thalassemias are a group of genetic disease caused by the production of unbalanced numbers of

Category: Philosophy - H