Chem 1120 Quiz 6

Instructions: This quiz is open-book. You may use any book, magazine, or other printed or web-based materials you feel are helpful. You may discuss this quiz with other members of this immediate class and section. You may not discuss, receive help on, or work on this quiz with tutors, friends, family members, or any one outside of class without my explicit permission. Violation of this stipulation is academic misconduct and is grounds for dismissal from class. You must work the quiz in its entirety by yourself before meeting in groups to compile a group quiz. I will award extra credit (5 pts) to those who work in groups of 2-5 and who submit a group quiz. You must show all your work for full credit, or to receive partial credit if you make a mistake.

1. (12 pts, 3 pts each) Draw the structure of each of the following tripeptides. Assume that these are found at a pH that will permit ionization of all ionizable functional groups.
1. Val-Gly-Leu
2. Arg-Lys-His
3. Tyr-Pro-Ser
4. Glu-Asp-Phe
2. (9 pts, 3 pts each) Interactions of amino acids on the interior of proteins are key to the shapes of proteins. In group (a) below, which pairs of amino acids would form hydrophobic interactions? In group (b) below, which pairs of amino acids would form ionic interactions? In group (c) below, which pairs of amino acids would form hydrogen bonds? Support your choices.

   	(a)	(b)	(c)
   1.	Pro. . . Leu	Arg. . . Asp	Gly. . . Ala
   2.	Arg. . . Thr	Cys. . . Met	Ala. . . Phe
   3.	Ile. . . Val	Gly. . . Ala	Cys. . . Cys
   4.	Tyr. . . Phe	His. . . Glu	Thr. . . Glu

3. (4 pts) The primary structure or sequence of peptides can be deduced by "overlap" in the sequence fragments that result from partial hydrolysis. If an octapeptide consists of 2 Phe, 2 Glu, 2 His, Asp, and Try, how many different possible configurations exist? If the following fragments are found after partial hydrolysis, what is the actual sequence?

   His-Tyr	Glu-Phe	Asp-His-Tyr
   Tyr-Glu-His	Phe-Glu-Phe	Glu-Phe-Asp