Download Discussion Problem Set 1. C483 Spring 2014

Discussion Problem Set 1. C483 Spring 2014
Problems from lectures 4 and 5 1/22/14, and 1/24/14
1. What are the categories of amino acids? Which amino acids may be thought of in
more than one category? Explain.
2. Which two amino acids are helix-breaking? Why?
3. Draw a titration curve for alanine. Indicate in your diagram all relevant pKa’s and
the pI. Define pI.
4. What is the most common amino acid modification in mammalian proteins? Draw
the structure of this amino acid.
5. The pKa’s of the alpha-carboxyl group in amino acids are about 2 pKa units lower
than acetic acid. Explain.
6. Draw a tetrapeptide of the following structure: N,W, E, Q
7. Do you expect the pKa of the alpha amino group in Lys and Arg to be lower or
higher than of Ala? Why?
8. Do you expect the pKa of the side chains in Glu and Asp to be higher or lower
than the alpha carboxyl group. Why?
9. What amino acids are used by muscles as a significant source of energy? What is
the byproduct formed by this process?
10. Collagen is thought to form triple helices in which H-bond donation from the
hydroxyproline plays a significant role. How might you test this? Be specific
(structures).
11. What molecule is used to funnel nitrogen from working muscles to the liver?
What does the liver do with these carbons?
12. Glutamate and aspartate are closely related to which Krebs cycle intermediates?
(structures)
13. What modification of proteins is most commonly used to control and regulate enzyme
activity? Which amino acids are most commonly modified?