MLAB 1315- Hematology Keri Brophy-Martinez

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MLAB 1315- HematologyKeri Brophy-Martinez

• Unit 6 Hemoglobin

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Hemoglobin

• What is it?
• Iron- bearing protein which is the main component
  of the RBC
• Gives the red cell its color
• Function
• Carry oxygen from the lungs to the tissues
• Remove CO2
• Buffering action, maintains blood pH as it
  changes from oxyhemoglobin (carrying O2) to
  deoxyhemoglobin ( without O2)

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Structure

• Structure
• Globin a tetramer of two pairs of unlike globin
  polypeptide chains
• 2 alpha (a) chains
• 2 beta (ß) chains
• 4 heme groups, each of which contains a
  protoporphyrin ring plus Fe . Iron can only
  bind oxygen in the ferrous (Fe) state.

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Structure

• Fe
• 
  Heme Globin HEMOGLOBIN
• Protoporphyrin

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Synthesis

• Synthesis
• Occurs in the cytoplasm of developing red cells
  as they mature in the bone marrow
• Processes necessary for normal synthesis
• Adequate iron supply delivery
• Adequate synthesis of protoporphyrins
• Adequate globin synthesis

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• Syntheis of hemoglobin in the reticulocyte
  (retic)
• Iron delivery supply
• Iron is delivered to the reticulocyte by
  transferrin a glycoprotein synthesized in the
  liver
• Excess iron aggregates in the cytoplasm as
  ferritin
• Synthesis of protoporphrins
• Begins in the mitochondria of the reticulocyte
• Mediated by erythropoietin and the presence of
  vitamin B6
• Protoporphyrin iron heme
• Excess formation of porphyrin results in
  metabolic disorders called porphyrias

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• Globin synthesis
• Globin chain synthesis occurs on the ribosomes of
  the reticulocyte.
• The rate of globin synthesis is proportional
  to the rate of porphyrin
• synthesis.
• Excess accumulated iron in the nucleated RBC
  (NRBC) results in a cell called a sideroblast.
• A siderocyte is a red blood cell (anucleated)
  with excess iron
• Proper globin synthesis depends on genes. The
  precise order of amino acids in the globin
  chains is critical to the structure and function
  of hemoglobin. (More discussion to follow in
  another section.)
• Chain designations are as follows
• Alpha a, beta ß, delta d, epsilon e, gamma ?,
  zeta?

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Normal hemoglobins and adult percentages

• Embryo
• Gower 2 a2e2
• Gower 1 a2e2
• Portland ?2?2
• Fetus
• F a2?2 1-2
• Adult
• A a2ß2 95-97
• A2 a2d2 2-3

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Abnormal hemoglobins

• Carboxyhemoglobin
• Oxygen molecules bound to heme are replace by
  carbon dioxide.
• Slightly increased levels of carboxyhemoglobin
  are present in heavy smokers and as a result of
  environmental pollution.
• Can revert to oxyhemoglobin.
• Methemoglobin
• Iron in the hemoglobin molecule is in the ferric
  (Fe3) state instead of the ferrous (Fe2) state.
  Incapable of combining with oxygen.
• Can occur as a result of strong oxidative drugs
  or to an enzyme deficiency (more discussion to
  follow).
• Can revert to oxyhemoglobin
• Sulfhemoglobin
• Hemoglobin molecule contains sulfur.
• Caused by certain sulfur-containing drugs or
  chronic constipation.
• Cannot revert to oxyhemoglobin and may cause
  death.