X-tra Problems_Hemoglobin_Brandon_key

X-tra Problems_Hemoglobin_Brandon_key - 1.) The plots below...

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1.) The plots below show the relationship of fractional saturation (Y) to oxygen concentration. Label each curve as A, B, C or D. Curve A: normal adult human hemoglobin under conditions in which P50 = about 40 torr. Curve B: normal adult human hemoglobin at a lower pH than curve A. Curve C: a mutant human hemoglobin which exists only in the R conformation; it cannot undergo a conformational shift to the T state. Curve D: a mutant human hemoglobin in which the T - R conformational equilibrium is strongly shifted toward the T state. 2.) Hb Ohio is a mutant human hemoglobin with residue β142 mutated from Ala -> Asp. Asp-142 contacts the β−cleft positioned next to His-143 (Ser-143 in fetal Hb). A. Briefly explain what effect the you would expect the Ala -> Asp mutation to have on the binding affinity of Hb Ohio for 2,3-bisphosphoglycerate at pH 7.4, compared with the affinity of normal adult human hemoglobin for 2,3-BPG. Ans: Hb Ohio would have a lower binding affinity for 2,3-BPG than normal adult Hb in the blood cells. The mutant residue has introduced a negative charge into the central cavity adjacent to a positively charged residue (His 143) involved in binding the multiply negatively charged 2,3-BPG by charge- charge interactions. The mutation would be expected to reduce the binding affinity for 2,3-BPG due to the loss of positive charge in the binding cavity. B. Would you predict that the mutant Hb Ohio would have a higher or lower O2 affinity than normal HbA in the red blood cells? Briefly explain your reasoning. Hb Ohio would have a higher binding affinity for O2 in the red cells, because the mutation has a lower binding affinity for 2,3-BPG and thus the T-R equilibrium would be shifted toward the R state in the red cells, which is the high O2 affinity conformation, so Hb Ohio would have a higher binding affinity for O2.
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This note was uploaded on 02/02/2010 for the course BIOCHEM Biochem440 taught by Professor Dr.klevit during the Winter '09 term at University of Washington.

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X-tra Problems_Hemoglobin_Brandon_key - 1.) The plots below...

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