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Chapter 21 733
Copyright © 2017 Pearson Education, Inc.
Chapter 21 Practice Test
1.
Draw the structure of the following amino acids at pH
=
7:
a.
glutamic acid
b.
lysine
c.
isoleucine
d.
arginine
e.
asparagine
2.
Draw the form of histidine that predominates at:
a.
pH
=
1
b.
pH
=
4
c.
pH
=
8
d.
pH
=
11
3.
Answer the following:
a.
Alanine has a pI
=
6.02, and serine has a pI
=
5.68. Which will have the highest concentration of
positive charge at pH
=
5.50?
b.
Which amino acid is the only one that does not have an asymmetric center?
c.
Which are the two most nonpolar amino acids?
d.
Which amino acid has the lowest pI?
4.
Why does the carboxyl group of alanine have a lower p
K
a
than the carboxyl group of propanoic acid?
alanine
p
K
a
=
2.2
p
K
a
=
4.7
propanoic acid
CH
3
CH
2
CH
3
CH OH
OH
NH
3
+
C
O
C
O
5.
Indicate whether each of the following statements is true or false:
a.
A cigar-shaped protein has a greater percentage of polar residues than a
spherical protein.
T
F
b.
Naturally occurring amino acids have the l-configuration.
T
F
c.
There is free rotation about a peptide bond.
T
F
6.
What compound is obtained from mild oxidation of cysteine?
7.
Define each of the following:
a.
the primary structure of a protein
b.
the tertiary structure of a protein
c.
the quaternary structure of a protein