Hemoglobin
In biology, hemoglobin is the iron-based, oxygen-carrying protein molecule of red blood cells. These protein structures are found in all vertebrates and some invertebrate organisms. The structure of the metalloprotein differs between species.[1]
In mammals, the chromoprotein makes up about 96% of the red blood cells' dry content (by weight), and around 35% of the total content (including water). Hemoglobin increases the total blood oxygen capacity 70-fold compared to capacity in blood without hemoglobin. The mammalian hemoglobin molecule can carry up to four oxygen molecules.
Hemoglobin is involved in the transport of other gases: It carries some of the body's respiratory carbon dioxide (about 20–25% of the total), in which CO2 is bound to the heme protein. The molecule also carries the important regulatory molecule nitric oxide, releasing it at the same time as oxygen.
Human hemoglobins
Embryos
The normal human embryo hemoglobin has two ζ-chains and two ε-chains.
Fetuses
In human fetuses the normal hemoglobin is Hemoglobin F (also called Hemoglobin F). Hemoglobin F has "two alpha and two gamma polypeptide subunits in comparison to normal adult hemoglobin, which has two alpha and two beta polypeptide subunits. Fetal hemoglobin concentrations can be elevated (usually above 0.5%) in children and adults affected by leukemia and several types of anemia."[2]
Adults
The normal adult human hemoglobin is Hemoglobin A. This hemoglobin consists of two alpha and two beta chains.[3] A less common hemoglobin found in normal adults is Hemoglobin A2. Hemoglobin A2 is an "adult hemoglobin component normally present in hemolysates from human erythrocytes in concentrations of about 3%. The hemoglobin is composed of two alpha chains and two delta chains. The percentage of HbA2 varies in some hematologic disorders, but is about double in beta-thalassemia."[4]
Genetics
Normal hemoglobins
Most humans carry:[5]
- "two α-globin genes on chromosome 16"
- "two γ-globin genes on chromosome 11"
- "a single δ-globin gene, and a single β-gene on chromosome 11"
References
- ↑ Anonymous (2024), Hemoglobin (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Anonymous (2024), Hemoglobin F (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Anonymous (2024), Hemoglobin A (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Anonymous (2024), Hemoglobin A2 (English). Medical Subject Headings. U.S. National Library of Medicine.
- ↑ Attar EC, Hasserjian RP (May 2006). "Case records of the Massachusetts General Hospital. Case 14-2006. A 25-year-old woman with anemia and iron overload". The New England journal of medicine 354 (19): 2047–56. DOI:10.1056/NEJMcpc069005. PMID 16687718. Research Blogging.