Organic Chemistry III

Professor Carl C. Wamser

Chapter 27 Quiz

1. (4 points) Write a complete structure for the tripeptide Arg-Asn-Trp , as it would be expected to appear at pH 7.

2. (3 points) Illustrate possible side-chain interactions as indicated:

a) H-bonding between His and Thr

b) covalent bonding between Glu and Lys

c) charge-dipole attraction between a C-terminal Ala and Tyr

3. (3 points) Describe the results of the action of each of the following on Ala-Pro-Trp-Lys-Gly .
(Full structures are not needed - just cite the amino acids or peptides that are affected or produced.)

a) Edman reagent

releases N-terminal Ala as PTH derivative

b) carboxypeptidase

releases C-terminal Gly

c) t-BuOCOCl

protects N-terminal Ala and Lys side chain amine

d) trypsin

cleaves at Lys to give Ala-Pro-Trp-Lys and Gly

e) chymotrypsin

cleaves at Trp to give Ala-Pro-Trp and Lys-Gly

f) ethanol, HCl

forms ethyl ester at C-terminal Gly