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L20 462a_hemoglobin3_lec20_2012

L20 462a_hemoglobin3_lec20_2012 - Protein function and...

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Protein function and ligand binding: Hemoglobin 3 Hemoglobin Func.on: Fetal Hb Mutant Hemoglobins Lec 20 (L20) Bioc 462A October 8, 2012
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Key Concepts Fetal Hb (HbF) ( α 2 γ 2 ) has different quaternary structure from adult HbA ( α 2 β 2 ). Sequence difference between β and γ reduces HbF’s affinity for 2,3‐BPG, thus increasing its affinity for O 2 . HbS: surface amino acid subs.tu.on ‐‐> aggrega.on Examples of other mutant hemoglobins with proper.es altered in one of the following ways: Muta.on in heme binding pocket leads to loss of heme. Muta.on disrupts ter.ary structure of a subunit. Muta.on stabilizes methemoglobin (Fe 3+ oxida.on state of heme in Hb). Muta.on stabilizes R state, or stabilizes T state, compared with their normal stabili.es in normal HbA.
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Explain why maternal red blood cells release O 2 and fetal red blood cells bind O 2 in the placenta, including a) difference in quaternary structure (subunit composi.on) and in protein primary structure between HbA and HbF; b) effect of protein structural difference on 2,3‐BPG binding affinity; c) resultant difference in O 2 binding proper.es between HbA and HbF under physiological condi.ons, i.e. at the 2,3‐BPG concentra.on in erythrocytes in the placenta. Describe the molecular defect in sickle cell anemia and how/why deoxyHbS molecules aggregate. Predict the effect of a hemoglobin muta.on on the O 2 binding proper.es of the mutant protein, given informa.on about nature/loca.on of the muta.on (amino acid subs.tu.on). See examples in lecture notes and in Ch.5 problem #7 in textbook. Learning Objec:ves
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Delivery of O 2 from maternal Hb to fetal Hb In vivo, O 2 must diffuse across the placenta from maternal red cells (in maternal circula.on) to fetal red cells (in fetal circula.on).
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