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9 Cards in this Set
- Front
- Back
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Hemoglobin structure
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-4 ploypeptides ea. has its own heme:
adult hemeoglobin=alpha 2,beta 2 (HbA) minor adult hemo=alpha 2 sigma 2 (HbA2) fetal=alpha 2, gamma2 (HbF) -subunits interact by salt bonds and h bonds -histadine that also binds w/ Fe -Fe on heme can only bind O2 in the ferrous state Fe2 -apoprotein protects heme from oxidation -distal histidine dec Hgb affinity for CO |
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Methemoglobin
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-nonfunxnal oxidized form of Hgb
-useless as an O2 xporter -can't bind O2 b/c is in the ferric state Fe3 |
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How methemoglobin happens
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-poisoning w/ oxidizing agents i.e. chlorox
-overprod of oxidants by enzymes -failure of a cell to make intracellular reductants -congenital replacement of the proximal histidine of Hb by tyrosine -failure of the enzyme methemoglobin reductase can be tx w/ reducing agent like methylene blue |
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Carbon monoxide
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-competitive agonist
-binds to heme instead of O2 -binds irreversibly to Hgb (cyanosis)cherry red -tx w/ hyperbaric O2 |
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Allosteric properties
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alternative conformations:
R(relaxed)=oxyheme T (tense)=deoxyhem O2 binding breaks salt bonds b/t subunits and rearranges h bonds changing the structure from T to R |
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Positive cooperativty
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R has a inc affinity for O2 so there's a + cooperativity b/t 2 O2 binding sites:binding of O2 to 1 heme inc the affinity of the 3 other hemes
-shows a sigmoidal curve @ p50 oxygen carrier is 1/2 sat w/ o2 @ torr of 26 -o2 is a ligand for heme -myoglobin has a hyperbolic curve and it's torr at 1/2 sat is 1 |
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Negative cooperativity
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2,3 bisphosphoglycerate:
binds to beta chains in T form which lowers the o2 affinity |
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Bohr effect
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-dec PH dec o2 binding affinity of hgb this shifts curve to right, stimulates o2 delivery
-co2 causes o2 to be released in active tissues i.e. muscles |
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Fetal hgb
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has an inc o2 affinity for o2 than HbA b/c BPG is less tightly bound than in adults allows o2 to go from mom to baby
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