Hemoglobin

Hemoglobin is the oxygen carrying substance in the blood. It is found in the red blood cells, and it is what gives blood its red color. It is a complex molecule consisting of 4 globin chains (polypeptide chains or proteins) with a heme group inserted into each globin "pocket". The heme group consists of a porphyrin ring and an iron (Fe) atom occupying the center of the ring. It is the iron atom that binds oxygen for transport through the blood. One hemoglobinn molecule carries 4 oxygen molecules.

Hemoglobin in 3D. This is an excellent site that displays a rotating hemoglobin molecule in 3D. (You will need chime software to view it which you can download from the site.)

The normal human hemoglobins found at different stages of development are encoded for by 6 different structural genes resulting in 6 globin (polypeptide) chains: alpha , beta , gamma , delta , epsilon , and zeta .

Normal adult hemoglobin (HbA) contains 2 globin chains and 2 globin chains.

Fetal hemoglobin (HbF) contains 2 and 2 globin chains.

The embryonic hemoglobins, Gower 1 (), Gower 2 () and Portland (), are synthesized in the very early embryo. At about 8 weeks of gestation the fetal liver takes over synthesizing predominantly HbF () and a small amount of HbA ().

An infant is born with approximately 70% HbF. The level normally falls to about 1% within the first year of life.

A normal adult will typically have:

HbA		>96%
HbF		<1%
HbA2		<3.5%

Elevated HbA₂ is characteristic of beta-thalassemia trait.

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