..... Click the link for more information. cells (erythrocytes) of all vertebrates and some invertebrates. A hemoglobin molecule is composed of a protein group, known as globin, and four heme groups, each associated with an iron atom.
In the lungs, each iron atom combines reversibly with a molecule of oxygen. Each hemoglobin molecule also has attached a single cysteine amino acid, which attracts nitric oxide from the lungs. The enriched hemoglobin circulates and is carried through the body to the tissues, where the nitric oxide dilates the small capillaries, allowing hemoglobin to deliver its oxygen to the tissues. Then the oxygen- and nitric oxide–free hemoglobin molecule picks up carbon dioxide and free nitric oxide and transports both back to the lungs, where they are exhaled as waste.
Hemoglobin is produced in bone marrow Bone marrow transplantation is a technique that infuses healthy bone marrow into a patient whose bone marrow is defective. The transplant can be autologous, consisting of bone marrow removed from the patient, treated, and then reinserted, or it can be allogeneic, consisting of
..... Click the link for more information. by erythrocytes and is circulated with them until their destruction. It is then broken down in the spleen, and some of its components, such as iron, are recycled to the bone marrow. Other components, such as the heme groups, are broken down into bilirubin, transported to the liver, and secreted with the bile bile, bitter alkaline fluid of a yellow, brown, or green color, secreted, in man, by the liver. Bile, or gall, is composed of water, bile acids and their salts, bile pigments, cholesterol, fatty acids, and inorganic salts.
..... Click the link for more information. into the intestine for eventual elimination from the body.
Hemoglobin deficiency may be a result of structural abnormality in the hemoglobin molecules themselves. In sickle cell disease sickle cell disease or sickle cell anemia, inherited disorder of the blood in which the oxygen-carrying hemoglobin pigment in erythrocytes (red blood cells) is abnormal.
..... Click the link for more information. , this structural abnormality creates malformed red blood cells which clog blood vessels, severely restricting the supply of blood flowing to body tissues.
hemoglobin
Protein in the blood of many animals (in vertebrates it is in red blood cells) that transports oxygen from the lungs to the tissues. It is bright red when combined with oxygen and purple-blue in the deoxygenated state. Each molecule is made up of a globin (a type of protein) and four heme groups. Heme, a complex heterocyclic compound, is an organic molecule derived from porphyrin with an iron atom at the centre. Variant hemoglobins (see sickle-cell anemia; hemoglobinopathy) can be used to trace past human migrations and to study genetic relationships among populations.
haemoglobin (US), hemoglobin
Hemoglobin
The oxygen-carrying molecule of the red blood cells of vertebrates. This protein represents more than 95% of the solid constituents of the red cell. It is responsible for the transport of oxygen from the lungs to the other tissues of the body and participates in the transport of carbon dioxide in the reverse direction.
Each molecule of hemoglobin comprises four smaller subunits, called polypeptide chains. These are the protein or globin parts of hemoglobin. A heme group, which is an iron-protoporphyrin complex, is associated with each polypeptide subunit and is responsible for the reversible binding of one molecule of oxygen. The polypeptide chains and the heme are synthesized and combine together in nucleated red cells of the bone marrow. As these cells mature, the nuclei fragment and the cells, now called reticulocytes, begin to circulate in the blood. After sufficient hemoglobin has been formed in the reticulocyte, all nuclear material disappears and the cell is then called an erythrocyte, or red blood cell. Each hemoglobin molecule lasts as long as the red cell, which has an average life of 120 days. See Porphyrin
Normal adult males and females have about 16 and 14 g, respectively, of hemoglobin per 100 ml of blood; each red cell contains about 29 × 10-12 g of hemoglobin. Red cells normally comprise 40–45% of the volume of whole blood.
The reversible combination of hemoglobin and oxygen can be represented by the reaction shown below. The equilibrium constants for each step are not the same because 
an oxygen molecule on one heme group changes the affinity of the other hemes for additional oxygen molecules. This alteration in binding affinity during oxygenation is called heme-heme interaction and is due to small changes in the three-dimensional structure of the molecule.
Hemoglobin combines reversibly with carbon monoxide about 210 times more strongly than with oxygen. This strong affinity for carbon monoxide accounts for the poisoning effects of this gas.
Hemoglobin binds carbon dioxide by means of free amino groups of the protein but not by the heme group. The reversible combination with carbon dioxide provides part of the normal blood transport of this gas. Hemoglobin serves also as a buffer by reversible reactions with hydrogen ions. The acidic property of oxyhemoglobin is greater than deoxygenated hemoglobin. The extra binding of hydrogen ion by deoxyhemoglobin promotes the conversion of tissue carbon dioxide into bicarbonate ion and thus increases the amount of total carbon dioxide which can be transported by blood. See Blood, Respiration
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