Hemoglobin: Difference between revisions

Hemoglobin is a protein that is located in red blood cells. It carries oxygen from the lungs to deliver to the tissues and returns carbon dioxide from the tissues to the lungs. <ref name=medicine> [http://www.medicinenet.com/hemoglobin/article.htm Hemoglobin]  Siamak Nabili. MedicineNet.com </ref> Hemoglobin is made from two similar proteins, alpha and beta, that are connected together. Since each alpha and beta has another two protein molecules, Hemoglobin is actually made up of four protein molecules, which is also called globulin chains. Usually, the normal adult hemoglobin molecule includes 2 alpha-globulin chains and 2 beta-globulin chains. On the other hand, for infants, the hemoglobin molecule contains 2 alpha chains and 2 gamma chains. However, as the infant grows, 2 gamma chains are developed to 2 beta chains. Each different globulin chain holds the heme molecule, which is iron that transports the oxygen and carbon dioxide in blood. Because of the presence of the heme molecule, blood has red color. Also, hemoglobin helps to build the shape of the red blood cells.

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. 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. 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.

Hemoglobin variants are abnormal forms of hemoglobin. Since hemoglobin is made up of heme, an iron-containing portion, and globin, which forms a protein, the molecules are found in all red blood cells. The molecules bind oxygen in the lungs and carry it throughout the body to release it to the body’s tissues.