Page 1
1.
What is dicyclohexylcarbodiimide (DCC) used for in peptide synthesis?
A)
DCC protects the amino group of the intended N-terminal amino acid.
B)
DCC activates the carboxyl group toward nucleophillic attack.
C)
DCC cleaves the blocking groups from the final peptide.
D)
DCC is the resin (solid support) used to anchor the growing polypeptide.
E)
DCC removes the peptide from the resin at the conclusion of the synthesis.
2.
Which of the following amino acids is theoretically capable of existing in two
diastereomeric forms?
A)
Cysteine
B)
Threonine
C)
Leucine
D)
Serine
E)
Tryptophan
3.
Why is the following not a good two step route for the preparation of pure L-alanine?
CH3CH2CO2H + Br
2
catalytic
PBr3
excess
NH3
A)
The bromination is not selective (the CH3 and CH2 groups are both brominated).
B)
Ammonia is not sufficiently nucleophillic to react with a secondary bromide.
C)
Only the CH3 group is brominated.
D)
The product will be racemic.
E)
Propanamide would be the major product.
4.
Disulfide bonds in proteins
A)
result from oxidation of thiols (RSH).
B)
function to help maintain the shape of proteins.
C)
can be broken by reduction reactions.
D)
link two cysteine amino acid residues.
E)
All of these are true.
5.
Which amino acid does not form a characteristic blue color with ninhydrin?
A)
Cysteine
B)
Lysine
C)
Proline
D)
Valine
E)
Tryptophan
Page 2
6.
What material can be used repetitively (on a given sample) to sequence a polypeptide
from the N-terminal end?
A)
Chymotrypsin
B)
Sanger reagent
C)
Trypsin
D)
Edman reagent
E)
Carboxypeptidase
7.
How many tripeptides containing one residue each of L-alanine, L-valine, and glycine
are possible?
A)
2
B)
3
C)
4
D)
6
E)
9
8.
Which of the following is least likely to be found in nature?
A)
NCO2H
H
H
B)
C)
(S)-HOCH2CH CO2H
NH2
D)
(CH3)2CH C
H
CO2H
NH2
E)
(R)–CH3CH CO2H
NH2
9.
Which amino acid does not have an enantiomer?
A)
Alanine
B)
Glutamine
C)
Histidine
D)
Aspartic acid
E)
Glycine
Page 3
10.
How many amino acid residues are present in the following polypeptide?
NCH CNH CH CNH CH CNH CH
O O O O
CNH
CCH2
CH2OH
CH2CH2CH2NH C
O
CH
CH2
H2C
H2C C
O
NH2
CH2
CH2
H
O
A)
4
B)
5
C)
6
D)
7
E)
8
11.
What would be the abbreviated name of the following polypeptide?
H2NCH CNH CH CNH CH CNH CH
O O O O
C N
CH2
CO2H
CH2
OH
CH
CH2
CH3
CH2CH2
CNH2
O
HC
H3C
CH3
A)
val-thr-glu-ala-gln
B)
ala-thr-glu-val-gln
C)
met-ser-asp-leu-pro-NH2
D)
ala-ser-asp-val-gln
E)
ala-ser-asp-val-pro-NH2
Page 4
12.
It was not until 1974 that -carboxyglutamic acid (shown below) was discovered (by
researchers at the University of Colorado) in polypeptides. Based on your knowledge
of organic chemistry, what is the most likely reason that this particular amino acid
escaped identification so long?
CH CH2CH COH
O
HO2C
HO2CNH2-carboxyglutamic acid
A)
It tended to spontaneously form a cyclic anhydride:
B)
It tended to spontaneously lose carbon dioxide:
C)
It easily underwent a reverse-Knovenagle reaction:
D)
It tended to spontaneously form a cyclic amide (lactam):
E)
It was simply too polar to extract into non-polar organic solvents.
Page 5
13.
The artificial sweetener aspartame is a derivative of the dipeptide asp-phe. If
aspartame (asp-phe) was prepared from racemic amino acids, how many stereoisomers
(diastereomers + enantiomers) could be formed?
HO C
O
CH2CH
NH2
C
O
NCH
CH2
HC6H5
C
O
OCH3
Aspartame
A)
2
B)
3
C)
4
D)
6
E)
8
14.
Chymotrypsin catalyzes hydrolysis of peptide bonds where?
etc. C NH CH CNH etc.
O O
R
residue in question
“amino end” “carboxy end“
A)
At the carboxy end of residues with basic side chains
B)
At the amino end of residues containing aliphatic residues
C)
At the carboxy end of residues with aromatic side chains
D)
At the amino end of residues with aromatic side chains
E)
At the carboxy end of methionine residues
15.
The primary structure of a protein refers to the
A)
sequence of amino acids.
B)
overall 3-dimensional shape.
C)
localized shape of the backbone.
D)
degree of aggregation with other proteins.
E)
structure of the active site.
Page 6
16.
Which of the following amino acids would have the highest isoelectric point?
A)
Lysine
B)
Glutamine
C)
Aspartic acid
D)
Alanine
E)
Tryptophan
17.
Nearly all amino acids immediately release N2 gas upon diazotization (treatment with
aqueous HCl and sodium nitrite). Which amino acid would not?
A)
Lysine
B)
Histidine
C)
Tyrosine
D)
Cysteine
E)
Proline
18.
Why is the additional (ring) nitrogen in tryptophan not very basic?
N
H2C C
NH2
CO2H
H
H
A)
Cyclic amines are not basic.
B)
It is too far from the carboxyl group to be effected.
C)
Aromatic amines are weakly basic because of resonance.
D)
The additional amine group is offset by an additional carboxylic acid group.
E)
It is sp2 hybridized as therefore not as basic.
19.
What is the name of the DNA base shown?
N
NN
N
O
H
H
H2N
A)
Guanine
B)
Cytosine
C)
Adenine
D)
Uracil
E)
Thymine
Page 7
20.
In a DNA molecule, at which point would the base shown be attached to a deoxyribose
fragment?
N
NN
N
O
H
H
H2N
31
2
5
4
A)
1
B)
2
C)
3
D)
4
E)
5
21.
The difference(s) between DNA and RNA is (are):
A)
DNA incorporates 2-deoxyribose sugars rather than ribose.
B)
RNA is smaller than DNA.
C)
DNA uses thymine, RNA uses uracil.
D)
Two of the above are true.
E)
All of the above are true.
22.
Although traces of racemic amino acids have been found in meteorites, nearly all
naturally occurring amino acids on Earth have the stereochemistry shown. What is true
of this stereochemistry? (Assume R = alkyl)
RC
HCO2H
NH2
A)
Amino acids are of the (R) configuration.
B)
Amino acids are of the (S) configuration.
C)
Amino acids are not chiral.
D)
Amino acids are meso compounds.
E)
Amino acids easily change configuration.
Page 8
23.
Which attractive force is responsible for maintaining the tertiary structure of proteins?
A)
Disulfide linkages
B)
Hydrogen bonds
C)
Salt bridges
D)
Hydrophobic interactions
E)
All of these
24.
Which amino acid is responsible for the condition known as phenylketonuria (PKU)
which occurs in a small fraction of the population?
A)
Tryptophan
B)
Histidine
C)
Phenylalanine
D)
Proline
E)
Valine
25.
Which of the following statements is not true of amino acids?
A)
They are less acidic than carboxylic acids.
B)
In acid solution (pH ~ 2) they would show an IR absorption near 1720 cm-1.
C)
They are soluble in water but not in non-polar organic solvents.
D)
They are more basic than amines.
E)
In basic solution (pH ~ 12) they would show an IR absorption near 3300 cm-1.
26.
The organic portion of which of the following biological materials does not consist
mainly of polypeptides and/or proteins?
A)
Enzymes
B)
Hair
C)
Hemoglobin
D)
Membranes
E)
Insulin
Page 9
27.
What would result from the following reactions?
H3C C
O
HHCN heat ?
H3O+
NH3
A)
H2N C
H
H
C
O
OCH3
B)
H2N C
H
CH3
C
O
OH
C)
CH2C
H
H
C
O
OHH2N
D)
H2N C
H
H
CCH2N
E)
H3C C
H2N
CH3
C
O
OH
28.
Which nitrogen in the imidazole ring of histidine is the more basic?
H2N C
H
CH2
C
O
OH
N
N
H#2
#1
A)
#1
B)
#2
C)
both have same basicity
D)
neither is basic
E)
the histidine N-H is actually acidic
Page 10
29.
Which of the following represents how a typical amino acid would mainly exist in basic
solution (pH > 7)?
A)
CO2H
R
H2N H
B)
CO2–
R
H2N H
C)
CO2–
R
H3N H
+
D)
CO2H
R
H3N H
+
E)
None of the above.
30.
Which amino acid is shown?
CO2H
H2N H
CH2
OH
A)
Alanine
B)
Glycine
C)
Tyrosine
D)
Lysine
E)
Arginine
31.
Which of the following amino acids contains an aromatic ring?
A)
Alanine
B)
Serine
C)
Tyrosine
D)
Asparagine
E)
Glycine
Page 11
32.
Given that the pKa of the acidic form of proline is 2.0, and the pKa of the basic form of
proline is 10.6, what is the isoelectric point?
A)
2.0
B)
6.3
C)
4.4
D)
10.6
E)
7.0
33.
Amino acids are covalently bonded to each other through_______.
A)
hydrogen bonding
B)
disulfide bridges
C)
peptide bonds
D)
and folds
E)
None of the above.
34.
How many polypeptides would be present if the following was treated with trypsin?
CysGlyGluArgGlyP hePheTyrThrProLysAlaLeuTyr
A)
1
B)
2
C)
3
D)
4
E)
5
35.
Folding of polypeptides influenced by distant residues is an example of what protein
structure?
A)
Primary
B)
Secondary
C)
Tertiary
D)
Quaternary
E)
None of the above.
36.
The secondary structure of proteins is held together by hydrogen bonds between which
protein sub-structures?
A)
The C=O and N-H on amino acid side chains
B)
The C=O on the protein backbone and the N-H on the amino acid side chains
C)
The C=O on the amino acid side chains and the N-H on the protein backbone
D)
The C=O and the N-H on the protein backbone
E)
There are no hydrogen bonds involved with secondary structure.
Page 12
37.
At the isoelectric point, the amino acid alanine will exist as what structure?
A)
A positive ion
B)
A negative ion
C)
An uncharged molecule
D)
A zwitterion
E)
A carbocation
38.
What process would one use to make multiple copies of a fragment of DNA?
A)
Polymerase chain reaction
B)
Electrophoresis
C)
Transcription
D)
Translation
E)
Merrifield solid-phase synthesis
39.
Which of the following DNA base pairs can participate in Watson and Crick type
hydrogen bonding?
A)
A-T
B)
G-T
C)
G-C
D)
Both A and B
E)
Both A and C
Page 13
Answer Key