8/18/2019 Lecture 7 Sample Problem Answers

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Lecture 7 Sample Problem Answers 

1.  Would you expect the hemoglobin in a llama, a hoofed mammal native to the Andes ofSouth America, to have a higher or lower oxygen affinity than human hemoglobin?

You might expect it to be higher to compensate for the lower pO2 in the atmosphere butactually, the affinity is lower. A lower affinity allows a greater proportion of the O2bound by the hemoglobin to be released at tissue pO2. 

2.  The side chain of Asp 94 on the ! chain of hemoglobin is near the imidazole ring of His146 in the deoxy form of hemoglobin but not the oxy form.

a.  What kind of interaction would you expect to occur between Asp 94 and His 146

in deoxyhemoglobin?

Given that aspartate contains a carboxylic acid side chain and that the histidineimidazole can be protonated at physiologic pH, an electrostatic interaction would

be expected.

 b.  Aspartate 94 increases the pKa of histidine 146, what does this tell you about theinteraction of asp 94 and his 146?

 An increased pKa translates to needing a higher pH before the imidazole becomes

deprotonated. The effect stabilizes the electrostatic interaction.

3. 

In the mutant hemoglobin Hb Ohio (!142 Ala"Asp), the amino acid substitutiondecreases the stability of the !146 His-!94 Asp interaction. Draw the oxygen binding

curves for HbA and Hb Ohio to show the effect of the decreased stability of the !146

His-!94 Asp interaction on O2 binding?