Amino Acids and Peptides_PS3_F10

Amino Acids and Peptides_PS3_F10 - CHEM 4511 Problem Set 3...

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CHEM 4511 Problem Set 3 1. The citrulline isolated from watermelons has the structure shown below. Is it a D- or L-amino acid? Explain. 2. At a pH equal to the isoelectric point of alanine, the net charge on alanine is zero. Two structures can be drawn that have a net charge of zero, but the predominant form of alanine at its pI is zwitterionic. (A) Draw the two forms of alanine that could produce a net charge of zero. (B) Circle the one that is zwitterionic (C) Why is alanine predominantly zwitterionic rather than completely uncharged at its pI? (D) What fraction of alanine is in the completely uncharged form at its pI? Justify your assumptions. 3. Draw the structure of isoleucine. (A) How many chiral centers does it have? (B) How many optical isomers does it have? (C) Draw Fischer projections for all the optical isomers of leucine. 4. The titration curve of alanine shows the ionization of two functional groups with p K a values of 2.34 and 9.69, corresponding to the ionization of the carboxyl and the
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This note was uploaded on 11/04/2010 for the course CHEM 6501 taught by Professor Wendyl.kelly during the Fall '10 term at Georgia Tech.

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Amino Acids and Peptides_PS3_F10 - CHEM 4511 Problem Set 3...

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