Chapter 4—Amino Acids and the Peptide Bond
MULTIPLE CHOICE
1. The intrinsic properties of the 20 amino acids include all EXCEPT:
a.
-Carbon is symmetric.
b.
The capacity to polymerize.
c.
Novel acid-base properties.
d.
Varied structure and chemical functionality in side chains.
e.
Chirality
2. The amino and carboxyl groups of amino acids react in a head-to-tail fashion, eliminating water, and
forming a covalent ____ linkage typically referred to as a(n) ____ bond.
a.
ester, aromatic
b.
anhydride, phosphoanhydride
c.
amide, peptide
d.
dehydration, hydrogen
e.
none of the above
3. Because peptide bond formation is thermodynamically ____, biological systems must couple peptide
bond formation to a thermodynamically ____ reaction.
a.
favorable, favorable
b.
unfavorable, unfavorable
c.
favorable, unfavorable
d.
unfavorable, favorable
e.
none of the above
4. All of the statements about the classification of these amino acids are correct EXCEPT:
a.
Aspartic acid and asparagine are acidic amino acids.
b.
Alanine and valine are neutral, nonpolar amino acids.
c.
Serine and glutamine are polar, uncharged amino acids.
d.
Lysine and arginine are basic amino acids.
e.
Tyrosine and phenylalanine are aromatic amino acids.
5. The difference between serine and homoserine is the same as between cysteine and homocysteine.
This change from the common amino acid is:
a.
one additional methylene (−CH2−) group.
b.
one additional carboxyl group.
c.
two additional amine groups.
d.
presence of a ring system.
e.
one additional amine group.
6. Which of the following amino acids has more than one chiral carbon?
a.
serine
b.
lysine
c.
threonine
d.
cysteine
e.
aspartic acid
7. Which of the listed amino acids is classified as a basic amino acid?
a.
leucine
b.
phenylalanine
c.
aspartate
d.
asparagine
e.
lysine
8. All of the amino acids EXCEPT ____ have both free -amino and free -carboxyl groups.
a.
aspartic acid
b.
proline
c.
asparagine
d.
lysine
e.
valine
9. The amino acid with a side-chain pKa near neutrality and which therefore plays an important role as
proton donor and acceptor in many enzyme catalyzed reactions is:
a.
histidine.
b.
cysteine.
c.
proline.
d.
serine.
e.
methionine.
10. The pKa of the −carboxyl group of an amino acid is ____ by the presence on the amine group.
a.
greatly increased (>2 pH units)
b.
greatly decreased (> 2 pH units)
c.
unchanged
d.
slightly increased (1-2 pH units)
e.
slightly decreased (1-2 pH units)
11. Which statement about these amino acids and amino acid derivatives is correct?
a.
GABA (-aminobutyric acid) is a potent inhibitory neurotransmitter derived from aspartic
acid.
b.
Ornithine is an important metabolic intermediate found in the urea cycle.
c.
Epinephrine is a hormone derived from tryptophan.
d.
Serotonin is a neurotransmitter derived from tyrosine.
e.
Histamine is a neurotransmitter derived from glutamine.
12. At which of the following pH values would histidine (pKa values of 1.8, 6.0 and 9.2) be found with a
net negative charge?
a.
1.0
b.
4.0
c.
8.0
d.
11.0
e.
none of the above
13. What is the pH of a serine solution in which the −amine group (pKa 9.2) is 33% deprotonated?
a.
8.7
b.
8.9
c.
9.0
d.
9.5
e.
9.8
14. Glutamic acid has pKa values of 2.2, 4.3 and 9.7. Calculate the isoelectric point for glutamic acid.
a.
3.25
b.
4.3
c.
5.4
d.
7.0
e.
8.6
15. If the pI of a peptide is 4.6, ____ might be present while ____ would probably be absent.
a.
Glu / Lys
b.
His / Ser
c.
Arg / His
d.
Asp / Gly
e.
Cys / Tyr
16. An amino acid + an aldehyde → water + ?
a.
amide.
b.
ester.
c.
substituted amide.
d.
hemiacetal.
e.
Schiff base.
17. The pKa of the cysteine side chain ____ group is 8.32, so it is about 11% deprotonated at pH ____.
a.
acid, 3.2
b.
amino, 8.5
c.
hydroxyl, 10.2
d.
sulfhydryl, 7.4
e.
none of the above
18. Ninhydrin has all these properties EXCEPT:
a.
It reacts with an amino acid by oxidatively deaminating its amino group.
b.
It can be used to detect the location of amino acids following chromatography.
c.
It produces a purple colored product upon reaction with alanine.
d.
It produces a yellow product upon reaction with histidine.
e.
It can be used to quantify most amino acids.
19. All of the following react with the thiol group on cysteine EXCEPT:
a.
N-ethylmaleimide.
b.
iodoacetate.
c.
acrylonitrile.
d.
“Ellman’s Reagent“.
e.
benzaldehyde.
20. Which of the peptides would absorb light at 280 nm?
a.
Ala-Lys-His
b.
Ser-Gly-Asn
c.
Ala-Ala-Trp
d.
Val-Pro-Leu
e.
Ser-Val-Ile
21. Which of the following amino acids absorbs light most strongly between 250 and 300 nm?
a.
His
b.
Phe
c.
Trp
d.
Tyr
e.
None of the above absorb light in this range
22. All are true for stereoisomers EXCEPT:
a.
A diastereomer is a nonsuperimposable non-mirror image.
b.
An enantiomer is a nonsuperimposable mirror image.
c.
Diastereomers have different melting points.
d.
Diastereomers rotate plane polarized light in equal but opposite directions.
e.
None, all are true.
23. All are true statements about L-isoleucine EXCEPT:
a.
Its enantiomer is named D-isoleucine.
b.
L-alloleucine would be its diastereomer.
c.
It contains a total of two asymmetric or chiral carbons.
d.
It can also be named as (2S,3S)-isoleucine using the (R,S) system.
e.
Its diastereomer would be named D-leucine.
24. Using a cation exchange resin, a mixture of four amino acids is separated using an elution gradient of
increasing NaCl solution. What would be the correct elution sequence?
a.
Asp, Arg, Ser, Lys
b.
Arg, Asp, Lys, Ser
c.
Lys, Arg, Asp, Ser
d.
Asp, Ser, Lys, Arg
e.
Ser, Asp, Lys, Arg
25. When using a strongly acidic polystyrene resin (Dowex-50) chromatography column, the separation is
PRIMARILY by:
a.
ion exchange chromatography.
b.
gas-liquid chromatography.
c.
partition chromatography.
d.
liquid-liquid partition chromatography.
e.
none of the above.
26. Which of the following is classified as a neutral polar amino acid?
a.
Asp
d.
Ser
b.
Leu
e.
Trp
c.
His
27. For the peptide Ala-His-Glu-Val-Asp-Cys-Lys-Leu, what is the net charge at pH 3?
a.
-1
d.
+2
b.
0
e.
+3
c.
+1
28. Where C is the -carbon, N represents the amide nitrogen and Co is the carbonyl carbon of amino
acids in a peptide, the peptide backbone of a protein consists of the repeated sequence:
a.
−C−N−Co−
b.
−N−Co−C−
c.
−N−C−Co−
d.
−Co−C−N−
e.
none of the above
29. The peptide bond has partial ____ character.
a.
hydrogen bond
b.
double bond
c.
triple bond
d.
van der Waals bond
e.
all of the above
30. Which of the following IS NOT a result of resonance in peptide bonds?
a.
approximately 40% double bond (coplanar) character.
b.
restricted rotation in the peptide backbone at the N−C bond and C−Co bond.
c.
the coplanar six atoms of the peptide bond group of atoms.
d.
a C−carbon that is out of the coplanar group of atoms.
e.
Co−N bond distance that is shorter than normal, but longer than C=N bonds.
31. Which of the following atoms IS NOT contained within the amide plane of the peptide backbone?
a.
C-carbon.
b.
amide nitrogen.
c.
side chain carbons.
d.
carbonyl carbon.
e.
none, all are included.