Updated: 1/30/2017

Oxygen Transport and Hemoglobin

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Hemoglobin
  • Forms of O2 in Blood
    • dissolved O2
      • 2% of total O2 content
    • O2 bound to hemoglobin
      • 98% of total O2 content
  • Hemoglobin
    • a globular protein conisisting of 4 polypeptide subunits
      • 2 α subunits and 2 β subunits
      • binds 4 O2 molecules
        • each subunit contains a heme moiety (iron-binding porphyrin ring)
          • iron in heme moieties is in reduced, ferrous state (Fe2+)
            • Fe2+ binds O2 reversibly
    • exists in 2 states 
      • low O2 affinity T (taut) state
      • high O2 affinity R (relaxed) state
        • R state has 300x greater affinity for O2
    • exhibits positive cooperativity
      • binding of 1 O2 molecule to 1 subunit of deoxyhemoglobin increases affinity for O2 in adjacent subunits
      • sigmoidal shape of oxygen-hemoglobin dissociation curve is characteristic of positive cooperativity
Hemoglobin Variants
  • Hemoglobin F
    • fetal hemoglobin
    • 2 α subunits and 2 γ subunits (α2γ2)
      • ↑ affinity for O2, ↓ affinity for 2,3-BPG
        • facilitates O2 delivery from mother to fetus
  • Hemoglobin S
    • an abnormal variant of hemoglobin that causes sickle cell disease
      • α subunits are normal, β subunits are abnormal
      • forms sickle-shaped robs in red blood cells in deoxygenated form
        • distorts shape of red blood cells
          • can result in occlusion of small blood vessels
    • ↓ affinity for O2

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