CHM 365
Problem Set 2
Chapter 4
1. Draw the general structure of an amino acid in both the L and D configurations. Which configuration
would be found in nature?
2. Give the name, three-letter symbol, and one letter symbol of any nonpolar amino acid that contains an
alkyl group. Also, draw the entire amino acid structure for this amino acid.
3. Draw the peptide having the sequence GRTY in its predominant ionic form at pH 7.0.
4. Give at least two reasons why the chemical synthesis of peptides is important.
5. Several amino acids have side chains that are chemically active (can react during chemical synthesis)
and need to be protected during chemical synthesis. Give the name of three amino acids with side
chains that must be protected prior to synthesis and tell why this is necessary for each one.
6. Based on the pKa values given in your green handout, draw the predominant ionic structure of each of
the following amino acids at pH 3.0, pH 7.0, and pH 13.0.
a) Glycine
b) Glutamate
c) Asparagine
d) Arginine
e) Histidine
f) Proline
7. Calculate the isoelectric point (pI) of each amino acid in problem 6.
8. A solution contains a mixture of three peptides, YRS, EMF, and DPK. The α-COOH groups have a pKa
of 3.8: the α-NH3+ groups have a pKa of 8.5. At which pH value (2.0, 6.0, or 13.0) would
electrophoresis provide the best resolution of the three peptides in the mixture?
9. Calculate the pH at which the ε-amino group (last one in side chain) of lysine is 20% dissociated.
