<unk> , also spelled<unk>  and abbreviated<unk> , is the iron-containing oxygen-transport metalloprotein in the red blood cells of the blood in vertebrates and other animals. In mammals the protein makes up about 97% of the red cell’s dry content, and around 35% of the total content (including water).<unk>  transports oxygen from the lungs or gills to the rest of the body, such as to the muscles, where it releases its load of oxygen.<unk>  also has a variety of other gas-transport and effect-modulation duties, which vary from species to species, and may be quite diverse in invertebrates.
The name<unk>  is the concatenation of heme and globin, reflecting the fact that each subunit of<unk>  is a globular protein with an embedded heme (or haem) group; each heme group contains an iron atom, and this is responsible for the binding of oxygen through ion-induced dipole forces. The most common type of<unk>  in mammals contains four such subunits, each with one heme group. In humans, each heme group is able to bind one oxygen molecule, and thus, one<unk>  molecule can bind four oxygen molecules.
Mutations in the genes for the<unk>  protein in humans result in a group of hereditary diseases termed the<unk> opathies, the best known of which is sickle-cell disease. Historically in human medicine, sickle-cell disease was the first disease to be understood in its mechanism of dysfunction, completely down to the molecular level. However, not all such globin-gene mutations result in illness. These mutations are formally recognized as<unk>  variants rather than diseases. A (mostly) separate set of diseases involves underproduction of normal and sometimes abnormal<unk> s, through problems and mutations in globin gene regulation. These diseases, which also often produce anemia, are called thalassemias.<unk>  <unk>  is synthesized in a complex series of steps. The heme portion is synthesized in a series of steps which occur in the mitochondria and the cytosol of the immature red blood cell, while the globin protein portions of the molecule are synthesized by ribosomes in the cytosol. Production of<unk>  continues in the cell throughout its early development from the proerythroblast to the reticulocyte in the bone marrow. At this point, the nucleus is lost in mammalian red blood cells, but not in birds and many other species. Even after the loss of the nucleus in mammals, residual ribosomal RNA allows further synthesis of<unk>  until the reticulocyte loses its RNA soon after entering the vasculature (this<unk> -synthetic RNA in fact gives the reticulocyte its reticulated appearance and name).
The chemical empirical formula of the most common human<unk>  is  C738H1166N812O203S2Fe, but as noted above,<unk> s vary widely across species, and even (through common mutations) slightly among subgroups of humans.
Hemoglobin
Lipoprotein
Methaemoglobin
Albumin
Fetal hemoglobin
Beta globulins
Globulin
Gamma globulin