Can somone go over the last one Valine? where did they get the 9.62 from?
MCAT Student
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Answers
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Hi Mary - not sure where this question is coming from but it looks to be a typo to me. The pKa for the backbone amine in all amino acids are around 9, so the bottom line you have is correct. Also note - if the original pKa2 is actually 6.6, that would mean the pI of valine would be pretty acidic, and we know that valine, with a sidechain that can't be charged, is going to have a fairly neutral pI. If that question is from our resource, can you tell me where? I'll get that fixed :)
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Sorry for the confusion It's the Kaplan book biochem 9th Ed. The bottom line I screen shotted from the answers at the end of the chapter. The question gives PKa 1= 2.32 and PKa 2 = 6.62 and is asking to find the PI. The question did not provide the 9.62 is that something that we need to memorize or is it just a typo. Do we need to memorize any PKa values?
Thank you!
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Ah I see. It looks like that error has been correct in the most recent edition of the book (10th edition). You don't need to know specific pKa values, no, and based on your screenshot, that's a typo in an older edition. I would know more generically that pKa of carboxylic acid is around 2-3, and amines are around 8-9. Hope that helps!
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Got it thank you!
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