Consider the oligopeptide given below (written in the 3-letter code). Ser-Lys-Val-His-Gln-Asp Draw its full chemical structure on paper, as it would exist at pH = 7. Indicate all bonds (those to hydrogen are optional; you could use stick figures or write methylene as CH2 rather than H-C-H).

Draw the peptide below (full chemical structure), as it would exist at pH = 7. Indicate

all bonds (those to hydrogen are optional; you could use stick figures or write

methylene as CH2 rather than H-C-H). You do not need to indicate stereochemistry, but

make sure it is correct if you do.

b-

Examine the peptide you drew in Problem 1 and calculate its pI.

Given:

• The pK_a of the amino terminus is 9.2
• The pK_a of the carboxyl terminus is 1.88
• Assume that the pK_as of the side chains are the same as those of the free amino acids.

PI?

c.

Sketch a titration curve of the peptide from Problem 1, from pH = 0 to 14, using up to 5 equivalents of KOH. (Note: you might not have to use all 5 equivalents.) Mark the curve with the name of the amino acid side chain corresponding to each buffering region (or N-term or C-term for the N- and C-termini).

This problem is worth 3 points. You will upload it the same way as you will do for Problem 1.

You may use a print out of the titration curve provided in the print out or you can sketch it freehand using the picture below as a guide.

14 12 10 8 pH 6 4 2 0 O 1 2 3 4 5 equivalents of base