Organic Chemistry III
	Professor Carl C. Wamser
Chem 336 - Spring 2006	Quiz 27

1. (5 points) The nonapeptide shown below is oxytocin. Identify the nine amino acids (use the 3-letter abbreviations), listing from the N-terminus to the C-terminus.
(Hint - break the disulfide bond to better visualize the N-terminus)

N-terminus - _Cys_Tyr_Ile_Gln_Asn_Cys_Pro_Leu_Gly_ - C-terminus

(Note - the C-terminal carboxy group is an amide)

2. (2 points) The pKa values for His are 1.82, 6.00, and 9.17 .
Draw the structures of His as it would appear at pH 1, 4, 8, and 11.
(Stereochemistry at the alpha carbon is not necessary.)

3. (3 points) Show examples of side-chain interactions (NOT covalent bonding) that could occur between the following amino acids in a peptide. Write specific structures that show the interactions.

a) Lys and Glu

b) Tyr and Asn

c) Arg and Ser