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12 Cards in this Set

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O2 delivered to a tissue/organ is proportional to ________
to the difference in Y of Hb before and after blood perfuses tissue

deltaY = Y(artery)-Y(vein)
pO2 (and Y) in healthy lungs
100 torr; 0.98
Cooperative O2 binding
Small change in pO2 --> big change in Hb delta Y (esp in midrange, because of sigmoidal shape)
-binding of first O2 INCREASES O2 affinity
allosterism
binding of a molecule changes a different binding site
cooperativity
binding of molec X changes affinity for other X's. Type of allosteric site
quantitation of cooperativity
Y = (pO2)^n/((pO2)^n+(p50)^n)

n = degree of cooperativity (from 1 to max # of binding sites/molec)
Hb structure
-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)
Hb subunit movement on oxygenation
-Not much change within dimer; instead change in other dimer.
-other dimer rotates 15deg counterclockwise, breaking several intersubunit salt links
Iron movement & O2 bonding
-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
Breakage of ion pairs in Hb oxygenation
-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
deoxy Hb intersubunit ion pairs (salt links)
alpha lys 40 --> beta COO

alpha arg 141 --> alpha asp 126

there are two of both of these bonds (between dimers)
Two-state model of Hb allosterism
2 forms:
T (tense) form: Low O2 affinity, many intersubunit interactions

R (relaxed) form: High O2 affinity, few intersubunit interactions