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12 Cards in this Set
- Front
- Back
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O2 delivered to a tissue/organ is proportional to ________
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to the difference in Y of Hb before and after blood perfuses tissue
deltaY = Y(artery)-Y(vein) |
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pO2 (and Y) in healthy lungs
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100 torr; 0.98
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Cooperative O2 binding
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Small change in pO2 --> big change in Hb delta Y (esp in midrange, because of sigmoidal shape)
-binding of first O2 INCREASES O2 affinity |
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allosterism
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binding of a molecule changes a different binding site
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cooperativity
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binding of molec X changes affinity for other X's. Type of allosteric site
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quantitation of cooperativity
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Y = (pO2)^n/((pO2)^n+(p50)^n)
n = degree of cooperativity (from 1 to max # of binding sites/molec) |
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Hb structure
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-4 subunits, each with 1 heme
-held together by complementary interactions: ionic, h-bonds, nonpolar - Acts like a dimer of dimers (each dimer 1 alpha, 1 beta) |
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Hb subunit movement on oxygenation
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-Not much change within dimer; instead change in other dimer.
-other dimer rotates 15deg counterclockwise, breaking several intersubunit salt links |
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Iron movement & O2 bonding
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-In deoxyHb, irons are out of heme plane, pointing toward proximal his, so heme is distorted (dome-shape)
-When O2 bonds, irons come into heme plane, pulling proximal his, which pulls on attached polypeptide :. shape of subunit changes |
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Breakage of ion pairs in Hb oxygenation
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-pulled by his, 8 intersubunit ion pairs are broken
- O2 binding energy is driving force -1st binding drives more breakages, so O2 binding is weaker -breakages relieve strain |
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deoxy Hb intersubunit ion pairs (salt links)
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alpha lys 40 --> beta COO
alpha arg 141 --> alpha asp 126 there are two of both of these bonds (between dimers) |
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Two-state model of Hb allosterism
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2 forms:
T (tense) form: Low O2 affinity, many intersubunit interactions R (relaxed) form: High O2 affinity, few intersubunit interactions |
