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Function and Synthesis of Hemoglobin

Function and Synthesis of Hemoglobin

What is hemoglobin?

Hemoglobin is the main protein in mature red blood cells. Each RBC contains over 600 million hemoglobin molecules.  It is tetramer, that is, one molecule of hemoglobin in adult is composed of four globin chains, 2 alpha and 2 beta.  These chains are derived from chromosome, mainly chromosome 16 and 11.

Heme Structure of Hemoglobin

During the various stages of life such as embryonic, fetal and adult stages, different globin chains are expressed. During the fetal period, from about two months until birth, the dominant globin chain is alpha and gamma and this is known as fetal hemoglobin (HbF).

However, shortly after birth about 3-6months, one will notice a fall in fetal hemoglobin (HbF) and a there will be a rise in adult hemoglobin (HbA). An alteration to the alpha or beta globin will result in an abnormal hemoglobin.

What is the function of hemoglobin?

The major role of hemoglobin is to carry oxygen from the lungs to the tissues and return carbon dioxide (CO2) from the tissue to the lungs. It is the oxygen carrying component of RBCs.  Oxygen binds to hemoglobin with high affinity in an oxygen-rich environment and leaves hemoglobin in an environment where there is not enough oxygen.

Hemoglobin synthesis

The hemoglobin begins to be produced during the proerythroblast stage of the RBC cycle. The synthesis takes place in the mitochondria and ribosome by a series of biochemical reactions.

In the mitochondria, the synthesis of the heme portion of hemoglobin takes place. Here, heme synthesis begins with the condensation of glycine & succinyl-CoA to form δ-aminolevulinic acid (ALA). ALA then leaves the mitochondria and form porphobilinogen through a series of reaction forms coproporphyrinogen. This molecule then returns to the mitochondria and produce  protoporphyrin.

Proto-porphyrin is then combined with iron to form heme. Heme then exits the mitochondria and combines with the globin molecule which is synthesized in the ribosome.  A disruption at any point in the synthesis of hemoglobin can result in the following disorders:

  1. Iron deficiency anemia
  2. Lead poisoning
  3. Thalassemia
  4. Sideroblastic anemia

What are the normal ranges of hemoglobin in humans?

  • For  females the normal range for hemoglobin is : 11.5-15.5 g/dl
  • For  males the normal range for hemoglobin is : 13.5-17.5 g/dl

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