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The page below is a sample from the LabCE course Case Studies in Pediatric Hematology. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Hemoglobin Structure

A hemoglobin molecule is composed of four heme + globin chain units. Heme is an iron ion within a porphyrin ring structure. Globin chains are protein chains in the hemoglobin molecule. When four of these heme-globin chain units interact together, they form hemoglobin, the molecule responsible for transporting both inhaled oxygen to the tissues and carbon dioxide waste back to the lungs to be exhaled.
To review:
  • Heme = iron + porphyrin ring
    • Iron is the actual binding site for oxygen.
    • Since there are four hemes with one iron ion each in a hemoglobin molecule, each hemoglobin molecule can carry four molecules of oxygen.
  • Globin chain = a protein
    • One globin chain is associated with each of the four hemes in a hemoglobin molecule.
    • Globin protein chains are identified by Greek letters, such as:
      • Alpha (α)
      • Beta (β)
      • Gamma (γ)
      • Delta (δ)
Realize that there is not a single, universal hemoglobin molecule. Different combinations of globin chains produce different hemoglobin variants. Some of these variants are discussed on the next slide.