BICH 410, section 503, EXAM 1, Friday September 23, 1994


Please write your name on each page. Write concise answers and show your work in order to receive partial credit.

1. (10 pts) Amino acids. Fill in the blank with an appropriate amino acid (several answers are possible in some cases, but just write one).

2. (15 pts) You want to prepare a 0.1 M phosphate buffer at pH = 12.1. You have solutions of 0.1 M H3PO4, 0.1 M H2PO4-, 0.1 M HPO4-2, and 0.1 M PO4-3. Describe how you would prepare 1 liter of this buffer? The pKa’s of phosphoric acid are 2.14, 6.86, and 12.4. Please show your reasoning.

3. (10 pts) Name the 5 general types of chemical transformation reactions that occur in cells.

4. (15 pts) You are trying to separate a DNA-binding protein (protein X) from other proteins in a solution. Only three other proteins (A, B, and C) are present along with X. The proteins have the following properties:
proteinpImolecular wt.bind to DNA?
protein A7.782,000yes
protein B3.821,500yes
protein C7.923,000no
protein X7.822,000yes

What type of protein separation technique might you use to separate:
a) protein X from protein A?
b) protein X from protein B?
c) protein X from protein C?
For full credit, explain your reasoning.

5. (15 pts) Draw the structure of arginine in the L-configuration as it would appear at pH 7.

6. (10 pts) Draw the structure of two molecules of formamide (HCONH2) engaged in an optimally-oriented hydrogen bond.

7. (10 pts) Explain using a diagram why amphipathic molecules form micelles in water. In your answer describe what thermodynamic "force" drives micelle formation.

8. (15 pts) (a) Draw the titration curve of the dipeptide aspartyl phenylalanyl methyl ester (NutraSweet®). The C-terminal carboxyl is esterified with a methyl group. (b) At which of the following pHs (1, 7, or 12) do you expect this molecule to bind to an anion-exchange resin? Explain your reasoning.