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BR biology chapter 9 question 2

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2010premed

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HbS contains a valine residue at the beta 6 position, while HbA contains a glutamate residue

shows the figures of valine and glutamate, glutamate has an additional negative charge

In HbS, the pI is expected to be:
slightly greater than pI of HbA
slightly less than the pI for HBA

How do I go about answering this question? I think there may be an error in the answer key for this as well...

Thanks.
 

PiBond

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HbS contains a valine residue at the beta 6 position, while HbA contains a glutamate residue

shows the figures of valine and glutamate, glutamate has an additional negative charge

In HbS, the pI is expected to be:
slightly greater than pI of HbA
slightly less than the pI for HBA

How do I go about answering this question? I think there may be an error in the answer key for this as well...

Thanks.

the pI (isoelectric point) is just the pH at which the zwitterion is in greatest concentration. therefore, you need to ask yourself what the difference is between valine and glutamate? glutamate is an acidic AA while valine is a nonpolar one. knowing that when pH > pka, we have a deprotonated functional group we should be able to deduce the different states of HbS and HbA

overall, acidic amino acids have pI's lower than those of basic and nonpolar. put all that together and you've got an answer
 
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