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BL4010
PROBLEM SET 1
FALL 2007
1. Consider the ionization of histidine. Draw the structure at each ionization
state. Using the following pKa values, draw the titration curve and
calculate the pI.
backbone amino pKa = 8.0
backbone carboxyl pKa = 3.1
side chain amino pKa = 6.0
2. Draw the structure of the tripeptide P-I-R at pH=10. Identify the peptide
bonds. Label the alpha carbons, the N-terminus, and the C-terminus.
3. Calculate the pH of a 0.1 M solution of acetic acid (pKa = 2.3) when the
acid is one quarter ionized.
4. Calculate the pI of the peptide G-A-Q-H-S-R.
5. Draw hydrogen bonds between two antiparallel beta-sheets of
polyglycine.
6. You isolate a small peptide. Amino acid composition yields A,Y,Q,T,L,V,G
but treatment with trypsin and chymotrypsin fail to cleave the peptide.
Explain.
7. Draw the PTH derivative of tyrosine.
8. You are isolating a cytosolic protein from yeast. You are in the middle of a
gel filtration column when you realize that the electrode in the pH meter is
broken and your solution is pH 9 instead of pH 6.5. What are the
consequences to your experiment?
9. You isolate a novel nonapeptide. Given the following information, determine
the amino acid sequence. Write the final sequence using the single letter code.
Show work at each stage for partial credit. (24 points)
a) Hydrolysis and amino acid analysis yields: Gly, Lys, Val, Tyr, Leu, Glu, Met, NH4+
b) Treatment with phenylisothiocyanate yields:
N
N
H
S
H
O
BL4010
PROBLEM SET 1
FALL 2007
c) Treatment with either carboxypeptidase or staphylococcal protease yields: Tyr
d) Treatment with trypsin yields two products. Hydrolysis of the hexapeptide yields: Val,
Gly, Leu, Met, Lys. Treatment of the tripeptide with phenylisothiocyanate yields Gln.
d) Treatment with CnBr yields a hexapeptide and a tripeptide.
e) Treatment with chymotrypsin yields two products. Hydrolysis of the tetrapeptide
yields Met, Gly, Leu.