The pKa of the Carboxyl Group of Amino Acid! - USMLE Forums
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Old 07-16-2012
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Biochemistry The pKa of the Carboxyl Group of Amino Acid!

Hi, I have a tiny question,

When i encounter questions that ask the net charge of an amino acid in a given PH, I only get the shape of the aminoacid, so I can figure out the cooH and NH2, but in the question stem I get only the pka values successively 2.2, 9.2, 10.7 without specifications which pka for which NH2 or COOH?

So how can I determine the charge if I don't know which pka value for either cooh or nh2?


When i read the explanation, it says that pka for cooh is 2.2, how can i know this ? and why not 9.2 or 10.7?
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Old 07-16-2012
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The COOH carboxyl group is usually negatively charged and therefore it's acidic and has low pKa.
The amino group is usually positively charged and therefore it's alkaline and and has high pKa.

Read more here
http://www.web-books.com/MoBio/Free/Ch2A4.htm

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eveli55 (07-16-2012), hypermedic (07-18-2012), one_destiny (07-16-2012)
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Old 07-18-2012
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Thaaanks a lot sabio....u really made my day
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