To expand upon the excellent writeups already in this node, a hemoglobin molecule contains
heme as a
prosthetic group and is composed of four polypeptides. The types of these
polypeptide chains are called
alpha,
beta,
gamma, and
delta, and they affect the
structure and
function of the molecule.
Here are the different types of hemoglobin, based on their chain structures:
Hemoglobin A is the normal form of the protein hemoglobin which is found in adults. It is composed of two alpha chains and two beta chains.
Hemoglobin C is an abnormal version of the protein. The sixth amino acid of the normal beta chain, glutamic acid, is replaced by lysine in hemoglobin C. This mutation causes the red blood cells to be less flexible.
Hemoglobin E is also an abnormal version of the protein; it is most often found in people of Southeast Asian descent. E plays a role in medical conditions such as microcythemia and mild hemolytic anemia. The beta chain of the hemoglobin molecule is altered because of a mutation.
Hemoglobin F is the normal form of the protein which is found in the fetus.
Hemoglobin H is an abnormal version and is composed of four beta chains. The molecule has a very high affinity to oxygen, but is very inefficient at transporting it.
Hemoglobin S is an abnormal version. The sixth amino acid of the normal beta chain, glutamic acid, is replaced by valine with gluconic acid. This mutation causes the red blood cells to take on a sickle shape, and is the cause of the sickle cell trait condition (when the individual is heterozygous for this mutant hemoglobin) and the disease of sickle cell anemia (when the individual is homozygous for this mutant hemoglobin).
From the science dictionary at http://biotech.icmb.utexas.edu/