Prof. Charles McKenna Chem 519 Problem Set #1 January 29, 2002

Total: 60 Pts. Due: February 10, 2002 [11AM]

 1. (25) From the recent literature, explain the chemistries involved in a solid-phase peptide synthesis scheme using fmoc protecting/ deprotecting, EDC coupling and photochemical bead cleavage chemistries (not discussed in class). Explain relative advantages/ disadvantages to other available techniques.

2. (25) A peptide has the sequence DYHTIGQAN

1. Construct a spreadsheet to simulate its titration from pH 2-14.
2. Find the net charge at pH 6 and 8.
3. Estimate the pI.

 3. (5) A protein was purified to homogeneity. Determination of the molecular weight by molecular exclusion chromotography yields 60 kd. Chromatography in the presence of 6 M urea yields a 30-kd species. When the chromatography is repeated in the presence of 6 M urea and 10 mM b-mercaptoethanol, a single molecular species of 15 kd results. Describe the structure of the molecule.

4. (5) Proteins are quite stable. The lifetime of a peptide bond in aqueous solution is nearly 1000 years. However, the DGº' of hydrolysis of proteins is negative and quite large. How can you account for the stability of the peptide bond in light of the fact that hydrolysis releases much energy?