Ch 22 Amino Acids & Proteins
1. Identify the following amino acids:
O
O
+
a.
H3N
O
-
b.
N
O
O
-
O
c.
+
N
H
O
d.
O
O
-
O
+
NH3
+
NH3
NH3
O
-
NH2
f.
e.
O
+
NH3
-
-
+
H2N
O
NH
O
+
NH3
-
Ch 22 Amino Acids & Proteins
2. Draw L- and D-threonine.
Ch 22 Amino Acids & Proteins
3. Circle the correct answer:
a. If the pH < pKa
[HA] > [A-] [HA] = [A-]
b. If the pH > pKa
[HA] > [A-] [HA] = [A-]
c. If the pH = pKa
[HA] > [A-] [HA] = [A-]
[HA] < [A-]
[HA] < [A-]
[HA] < [A-]
Ch 22 Amino Acids & Proteins
4. Draw the predominant form of alanine as a
function of pH (from 0 to 14)
0
7
14
Ch 22 Amino Acids & Proteins
5. Calculate the pI of:
(assume the pKa’s of –COOH and –NH3+ groups are 2
and 9.5 respectively)
a. valine
b. aspartic acid (pKa of side chain = 3.9)
c. arginine (pKa of side chain = 12.5)
Ch 22 Amino Acids & Proteins
6. Circle the correct answer:
a.
b.
c.
d.
e.
f.
As pI increases, the AA is:
more basic or more acidic
If pH < pI, the AA is: net positive, net negative or neutral
If pH > pI, the AA is: net positive, net negative or neutral
If pH = pI, the AA is: net positive, net negative or neutral
At a given pH, the higher the pI, the AA is more:
positive or negative
At a given pH, the lower the pI, the AA is more:
positive or negative
Ch 22 Amino Acids & Proteins
Electrophoresis pH =5
7. For the following fingerprint obtained by
electrophoresis and chromatography, label the
amino acids (ser, glu, val, his, met, thr) that would
be at each spot:
chromatography 
Ch 22 Amino Acids & Proteins
8. Illustrate the synthesis of valine using the
different methods:
a. HVZ reaction with amination
b. Reductive amination
c. N-phthalimido synthesis (Gabriel & malonic
ester synthesis)
d. Strecker synthesis
Ch 22 Amino Acids & Proteins
9.Illustrate a peptide synthesis of val-ser-ala
using:
a. Reagents in solution
b.
Automated solid-phase (Merrifield) synthesis
Ch 22 Amino Acids & Proteins
10. A nonapeptide undergoes partial hydrolysis to
give peptides whose amino acid compositions are
shown below. Reaction of the intact nonapeptide
with Edman’s reagent releases PTH-Leu. What is
the sequence of the nonapeptide?
a. pro,ser
e. glu,ser,val,pro
b. gly,glu
f. glu,pro,gly
c. met,ala,leu
g. met, leu
d. gly,ala
h. his,val
Ch 22 Amino Acids & Proteins
11. Determine the amino acid sequence of a decapeptide from the
following results.
a. Acid hydrolysis gives ala, his, gly, 2 lys, 2 met, phe, ser, val
b. Carboxypeptidase B releases an amino acid, but carboxypeptidase A
does not
c. Edman’s reagent releases PTH-His
d. Cleavage with cyanogen bromide gives 1. his, lys, gly, met, ser
2. lys, val
3. ala, phe, met
e. Trypsin-catalyzed hydrolysis gives 1. gly, his, lys
2. ala, 2 met, lys, phe, ser, val
f. Chymotrypsin-catalyzed hydrolysis gives a hexapeptide and a
tetrapeptide