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Tutorial Protein Set 2
Matching
A)
B)
C)
D)
E)
F)
G)
H)
I)
J)
K)
L)
M)
uncharged
deprotonated
three
-amino group
two
C-terminus
lysine
racemic mixture
zero
protonated
isoleucine
tryptophan
phenylalanine
1. When a peptide bond is formed, an ______ reacts with a carboxylate group.
2. In the peptide Trp-Ser-Val, valine is at the ______.
3. At a pH above its pK, the phenolic group of tyrosine is ______.
4. At a pH below its pK
-amino group of lysine is ______.
5. At a pH below its pK
-carboxylate group of Asp is ______.
6. The net charge of the zwitterion form of Gly is ______.
7. Biological systems usually produce a single enantiomer, whereas chemical synthesis produces
a ______.
8. In the tripeptide Trp-Val-Phe, the N-terminal residue is ______.
9. In the tripeptide Lys-Pro-Ile, the C-terminal residue is _________.
10. In the tripeptide Lys-Pro-Ile, there are ______ charged groups at pH 7.
Multiple Choice
11. Which of the following amino acids has a charged polar side chain at pH 7?
A) Leu
B) Ala
C) Met
D) Trp
E) Glu
12. Which of the following amino acids has a sulfur atom in its side chain?
A) Asn
B) Ser
C) Phe
D) Met
E) Tyr
13. Which of the following amino acids has an uncharged polar side chain at pH 7?
A) Arg
B) Thr
C) Glu
D) Pro
E) Ile
14. At pH 7, arginine (pK
-amino 8.99, guanidino 12.48) would be
charged as follows:
-amino, +1 guanidino, +1 net charge
-carb
-amino, -1 guanidino, 0 net charge
-carboxylate, -amino, -1 guanidino, -1 net charge
D) -amino, +1 guanidino, +1 net charge
E) -amino, +1 guanidino, 0 net charge
15. At pH 7, aspartic acid (pK
-carboxylate 3.9 ) would
be charged as follows:
A) 0 -carboxylate, +1 -amino, 0 -carboxylate, +1 net charge
B) -1 -carboxylate, +1 -amino, -1 -carboxylate, -1 net charge
C) 0 -carboxylate, -1 -amino, 0 -carboxylate, -1 net charge
D) +1 -carboxylate, -1 -amino, +1 -carboxylate, +1 net charge
E) +1 -carboxylate, +1 -amino, +1 -carboxylate, +3 net charge
16. At pH 11, glutamic acid (pKs are would be charged as follows:
A) +1 -carboxylate, 0 -amino, +1 -carboxylate, +2 net charge
B) -1 -carboxylate, +1 -amino, -1 -carboxylate, -1 net charge
C) 0 -carboxylate, 0 -amino, 0 -carboxylate, 0 net charge
D) +1 -carboxylate, -1 -amino, +1 -carboxylate, +1 net charge
E) -1 -carboxylate, 0 -amino, -1 -carboxylate, -2 net charge
-carboxylate 4.07.
17. At pH 4, histidine (pK
-amino 9.33, 6.04 imidazole) would be
charged as follows:
-amino, -1 imidazole, 0 net charge
B) -amino, 0 imidazole, 0 net charge
-amino, -1 imidazole, +1 net charge
D) -amino, +1 imidazole, +1 net charge
-amino, +1 imidazole, +2 net charge
18. At pH 5, cysteine (pK
-amino 10.7, sulfhydryl 8.37 ) would be
charged as follows:
-amino, 0 sulfhydryl, 0 net charge
-carboxylate, -amino, -1 sulfhydryl, -1 net charge
C) -amino, +1 sulfhydryl, +1 net charge
D) -amino, 0 sulfhydryl, 0 net charge
E) +1 -carboxylate, -1 -amino, 0 sulfhydryl, 0 net charge
19. At pH 1, lysine (pK
charged as follows:
-carboxylate, B) C) +1 -carboxylate, +2
D) 0 -carboxylate, +1
E) +2 -carboxylate, +1
-
-
-amino, -amino, -2 net charge
-amino, +1 net charge
-amino, +2 -amino, +5 net charge
-amino, +1 -amino, +2 net charge
-amino, +1 -amino, +4 net charge
20. The disulfide bond between two cysteine molecules:
A) is a peptide bond.
B) is an ionic bond that is stable at physiological pH.
C) is a covalent bond formed by oxidation.
D) is a hydrogen bond between the two sulfhydryl groups.
E) is a weak ion-induced dipole attraction.
-amino 10.54 ) would be
21. What proportion of the 20 amino acids are considered to be nutritionally essential to lab
animals?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
22. Which of the following statements is/are true?
A) amino acids can be derived from purines and pyrimidines
B) purines and pyrimidines can be derived from amino acids
C) no protein contains every standard amino acid
D) A and C
E) B and C
23. The isoelectronic point of an amino acid is the point where:
A) The pK of the carboxylic acid is the same as the amino group
B) Sodium ions are attracted to the amino groups
C) the solubility of the amino acid is maximized
D) the amino acid racemizes
E) the amino acid carries no net electrical charge
24. Amino acid side-chain residues have:
A) a positive charge in every situation
B) pKs that assure the solubility of every protein
C) constant pKs no matter what aqueous environment they are found in
D) different pKs in peptides as compared to the free amino acids
E) polar functional groups
25. Asx refers to
A) a negatively charged aspartic acid
B) a positively charged asparagine
C) a dipeptide containing both aspartic acid and asparagine
D) either aspartic acid or asparagine
E) an unnatural amino acid formed on protein hydrolysis
26. The formation of a dipeptide from two amino acids requires:
A) side-chain complementarity
B) loss of water
-carbon
-carbon
E) base catalysis
27. The peptide AYDG has an N-terminal _________ residue.
A) glycine
B) glutamic acid
C) glutamine
D) aspartic acid
E) alanine
28. Which of the following tripeptides would be expected to be the most hydrophobic:
A) KYG
B) KYA
C) GYA
D) DYA
E) DYG
29. What is the abbreviation for the peptide valylarginylisoleucine?
A) Val-Arg-Ile
B) Val-Agn-Leu
C) Vln-Arg-Ile
D) Val-Agn-Isl
E) Vln-Arg-Leu
30. The least abundant amino acid in proteins is:
A) V
B) W
C) G
D) F
E) A
31. Zwitterions are:
A) amino acids
B) ionic molecules that are racemic
C) molecules that bear both negatively and positively charged groups
D) side chain carboxylate anions
E) delocalized ions
32. All the standard amino acids except ____ are optically active.
A) Pro
B) Arg
C) Trp
D) Gly
E) Phe
33. The __________ character of most standard amino acids causes solutions of amino acids to
rotate plane polarized light.
A) chiral
B) zwitterionic
C) polar
D) all of the above
E) none of the above
34. All amino acids derived from proteins have the same conformation as:
A) L-glyceraldehyde
B) dextro-glyceraldehyde
C) D-glucose
D) cis-lysine
E) glycine
35. Typically, ‘unnatural’ amino acids with side chain modifications
A) are synthesized due to genetic mutations
B) are assembled by specialized bacterial enzymes
C) are formed by modification of standard side chain residues after the protein synthesis
D) are toxic
E) are racemic
36. An amide bond between a sideA) disulfide bond
B) amino amide bond
C) nor-peptide bond
D) isopeptide bond
E) hormone bond
-amino group is also called a(n):
Short Answer
39. Why can amino acid-binding proteins distinguish the enantiomeric forms of the free amino
acids?
38. Why do bacterial cell walls containing peptides with D-amino acids often escape digestion
by the proteases that other organisms use to kill bacteria?
Fill in the Blank
39. Histamine is formed from histidine by a ________ reaction.
40. _________ is a neurotransmitter formed from tyrosine by hydroxylation and
decarboxylation reactions.
41. Proline differs from the other 19 amino acids in proteins in that it has a _________ amino
group.