Deck 27: Amino Acids and Proteins

Question 1

Which of the following amino acids migrates to the positive electrode on paper electrophoresis at a pH of 7.0?

A) glutamic acid
B) arginine
C) lysine
D) histadine

Answer 1

glutamic acid

Question 2

Which of the following is a definition of the isoelectric point of an amino acid?

A) The pH at which an amino acid has no net charge
B) The pH at which the α-NH₂ group is completely protonated
C) The melting point of an amino acid
D) The conductivity of a 1 M solution of an amino acid in water

Answer 2

The pH at which an amino acid has no net charge

Question 3

Which of the following amino acids has an aromatic side chain?

A) tyrosine
B) glutamine
C) aspargine
D) valine

Answer 3

tyrosine

Question 4

What is the approximate value of the pK_a of the α-CO₂H of amino acids?

A) 2
B) 5
C) 9
D) 12

Question 5

Which of the following natural amino acids is an R-isomer?

A) cysteine
B) serine
C) valine
D) phenylalanine

Question 6

What are the R/S designations of the two stereocenters of isoleucine?

A) 2R,3R
B) 2R,3S
C) 2S,3R
D) 2S,3S

Question 7

Which of the following amino acids is a secondary amine?

A) proline
B) glutamine
C) cysteine
D) aspargine

Question 8

Which of the following amino acids has a sulfhydryl group?

A) serine
B) cysteine
C) lysine
D) tyrosine

Question 9

What is the approximate value of the pK_a of the α-NH₃⁺ of amino acids?

A) 2
B) 5
C) 9
D) 12

Question 10

Which of the following amino acids is not chiral?

A) leucine
B) glycine
C) alanine
D) proline

Question 11

Which of the following amino acids contains two stereocenters?

A) isoleucine
B) proline
C) phenylalanine
D) glutamine

Question 12

What is the isoelectric point of glutamic acid (pK_a of α-CO₂H, 2.10; pK_a of β-CO₂H, 4.07; pH of α-NH₂, 9.47)?

A) 3.08
B) 5.67
C) 6.16
D) 17.28

Question 13

Which of the following amino acids has an acidic side chain?

A) glutamine
B) glycine
C) glutamic acid
D) threonine

Question 14

Which of the following amino acids has a polar side chain?

A) isoleucine
B) valine
C) phenylalanine
D) threonine

Question 15

Which of the following amino acids has a non-polar side chain?

A) histidine
B) arginine
C) glutamine
D) valine

Question 16

Which of the following amino acids migrates to the negative electrode on paper electrophoresis at a pH of 7.0?

A) lysine
B) aspartic acid
C) asparagine
D) glutamic acid

Question 17

Which of the following amino acids is not an L-isomer?

A) serine
B) valine
C) glycine
D) proline

Question 18

Which of the following amino acids has a basic side chain?

A) lysine
B) serine
C) leucine
D) tyrosine

Question 19

What are the R/S designations of the two stereocenters of L-threonine?

A) 2R,3R
B) 2R,3S
C) 2S,3R
D) 2S,3S

Question 20

What is the isoelectric point of serine (pK_a of α-CO₂H, 2.21; pK_a of α-NH₂, 9.15)?

A) 5.68
B) 9.94
C) 11.36
D) 20.22

Question 21

The following structure is that of Sanger's reagent.

Question 22

Consider the following octapeptide.
Ala-Val-Trp-Lys-Phe-Gly-Arg-Met
The fragments that would be obtained by a trypsin hydrolysis are
Ala-Val-Trp-Lys and Phe-Gly-Arg and Met.

Question 23

Which of the following reagents can be used to cleave a benzyloxycarbonyl protecting group from a peptide?

A) HBr, CH₃CO₂H
B) conc. NaOH
C) heat
D) NaCl, H₂O

Question 24

Which of the following is not a polypeptide?

A) L-HIV-1 protease
B) hemoglobin
C) myoglobin
D) glycogen

Question 25

Valylalanine and alanylvaline are constitutional isomers.

Question 26

Which of the following tripeptides is not hydrolyzed by trypsin?

A) Glu-Arg-Ser
B) Arg-Glu-Thr
C) Glu-Ser-Arg
D) Lys-Ser-Arg

Question 27

How does phenyl isothiocyanate, Ph−N=C=S, react with a peptide in the Edman degradation?

A) the sp carbon acts as an electrophile in a reaction with an amino group of the peptide
B) the sulfur acts as a nucleophile and adds to the carbon of the peptide bond
C) the nitrogen acts as a nucleophile and adds to the carbon of the peptide bond
D) the sp carbon acts as an electrophile in a reaction with a carboxylate of the peptide

Question 28

Bradykinin is a nonapeptide, Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg. In addition to one mole of Arg, the following peptides are present after hydrolysis of bradykinin with chymotrypsin,
Arg-Pro-Pro-Gly-Phe-Ser and Pro-Phe

Question 29

Which of the bonds in the following structure is cleaved by cyanogen bromide?

A) i
B) ii
C) iii
D) iv

Question 30

To what structural feature does the term "quaternary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 31

To what structural feature does the term "secondary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 32

The molecule shown below is an α-amino acid.

Question 33

To what structural feature does the term "tertiary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 34

Which of the following dipeptides is L-Cys-L-Ala?

A) 1
B) 2
C) 3
D) 4

Question 35

To what structural feature does the term "primary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 36

Which of the following tripeptides is not hydrolyzed by chymotrypsin?

A) Phe-Lys-Glu
B) Lys-Tyr-Phe
C) Gln-Ser-Phe
D) Gln-Tyr-Ser

Question 37

What is the major organic product of the following reaction?

A) 1
B) 2
C) 3
D) 4

Question 38

Which of the following reagents can be used to cleave a benzyloxycarbonyl protecting group from a peptide?

A) H₂/Pd
B) H₂O
C) Na₂CO₃, H₂O
D) LiAlH₄

Question 39

Which of the following dipeptides is L-Ser-L-Phe?

A) 1
B) 2
C) 3
D) 4

Question 40

Ninhydrin is used to determine the N-terminal amino acid of a peptide.

Question 41

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is the product of an Edman degradation.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 42

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is an octapeptide with a C-terminal valine.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 43

The structure of the phenylhydantoin derived from the _____ cycle of the Edman degradation of Phe-Ala-Ser is

Question 44

For leucine the pI is the average of pK_a1 and pK_a2.

Question 45

Consider the following form of phenylalanine. This form would exist at a pH _______than the pI.

Question 46

Consider the following image. This represents the quaternary structure of a protein.

Question 47

In Phe-Ile-Ser-Asp-Gly-His-Gly-Tyr, the three-letter abbreviation for the C-terminal amino acid is ________.

Question 48

The Edman degradation is used to identify the ___-terminal amino acid of a peptide.

Question 49

The number of different combinations that are possible for a tripeptide containing one of each of the following amino acids: Phe, Val, Asp is ______.

Question 50

In Cys-Ile-Ser-Asp-Gly-His-Gly-Gly, the three-letter abbreviation for the N-terminal amino acid is ________.

Question 51

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is a peptide coupling reagent.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 52

Hydrogen bonds, α-helices, and pleated sheets are properties of structure of proteins.

Question 53

In terms of the number of amino acid residues Cys-Ile-Ser-Asp-Gly-His-Gly-Gly would be classified as a(n) ________________.

Question 54

Structure _____ (shown below) will migrate toward the positive electrode in an electrophoresis experiment.

Question 55

Structure _____ (shown below) will remain at the origin in an electrophoresis experiment.

Question 56

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is a polypeptide which gives four fragments on treatment with chymotrypsin.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 57

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is an amino acid in its zwitterionic form.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 58

MATCH a structure from the list below to each of the following terms. Place the letter of the structure in the blank to the left of the term which it describes.
_____ is a carboxyl-protected amino acid.

A)
B)
C)Val−Phe−Leu−Met−Tyr−Pro−Gly−Trp−Cys−Glu
D)
E)
F)Asp−Tyr−Ile−His−Pro−Phe−Arg−Val
G)BOC group
H)
I)
J)
K)
L)Val−Lys−Phe−Gly−Arg−Met−Arg−Phe
M)Z group

Question 59

Consider the following image. This represents the tertiary structure of a protein.

Question 60

A tetrapeptide contains the amino acids Phe, Ala, Gly, and Leu. Partial hydrolysis produces the dipeptides Phe-Ala, Ala-Gly, and Leu-Phe. The structure of the tetrapeptide is _________________________. Use the three-letter designations for the amino acids separated by dashes (-).

Question 61

In the Edman degradation analysis of the N-terminus of a peptide the terminal residue reacts with phenyl isocyanate, an example is shown below. Provide the structure of both of the products of this reaction.

Question 62

What fragments are produced when porcine dynorphin, a peptide that contains 17 amino acid residues (shown below), is cleaved with trypsin?
Tyr−Gly−Gly−Phe−Leu−Arg−Arg−Ile−Arg−Pro−Lys−Leu−Lys−Trp−Asp−Asn−Gln

Question 63

Edman degradation of the peptide saralasin shows that it has a sarcosine residue at the N-terminus.
Sarcosine is Partial hydrolysis of saralasin with dilute hydrochloric acid gives the following fragments:
His−Pro−Ala
Val−Tyr−Val
Arg−Val−Tyr
Sar−Arg−Val
Tyr−Val−His
What is the structure of saralasin?

Question 64

Identify the compound shown below. ​

A) L-Thyroxine
B) L-Triiodothyronine
C) L-Omithine
D) L-Citrulline

Question 65

Which of the following is not a strategy for the synthesis of polypeptides?

A) Protect the a-amino group of the amino acid aa1 to reduce its nucleophilicity so that the group does not participate in nucleophilic addition to the carboxyl group of either aa1 or aa2.
B) Cleave the polypeptide at specific peptide bonds, determine the sequence of each fragment, and then match overlapping fragments to arrive at the sequence of the polypeptide.
C) Activate the a-carboxyl group of the amino acid aa1 so that the group is susceptible to nucleophilic attack by the a-amino group of aa2.
D) Protect the a-carboxyl group of the amino acid aa2 so that the amino acid is not susceptible to nucleophilic attack by the a-amino group of another molecule of aa2.

Question 66

Provide the structure of Ser-Ala.

Question 67

Provide the structure of Ser-Phe-Asp.

Question 68

Identify the function of the following group in protein synthesis. ​

A) Protection
B) Hydrolysis
C) Hydrogenation
D) Alkylation

Question 69

The combination of the two sidechains of the given compounds leads to the formation of a special bond. Identify the type of bond formed. ​

A) Disulfide bond
B) Disulfite bond
C) Hydrogen bond
D) Vibrational bond

Question 70

Provide the structure of dicylcohexylcarbodiimide, a common reagent that is used to couple two amino acid residues by formation of a peptide bond, and the structure N,N'-dicyclohexylurea, the byproduct of this reaction.

Question 71

What fragments are produced when porcine dynorphin, a peptide that contains 17 amino acid residues (shown below), is cleaved with chymotropsin?
Tyr−Gly−Gly−Phe−Leu−Arg−Arg−Ile−Arg−Pro−Lys−Leu−Lys−Trp−Asp−Asn−Gln

Question 72

What are the products of the reaction of alanine and ninhydrin (shown below)?

Question 73

Which of the following is not an endopeptidase?

A) Trypsin
B) Chymotrypsin
C) Elastase
D) Carboxypeptidase A

Question 74

In the case of paper electrophoresis, a paper strip saturated with an aqueous buffer of predetermined pH serves as a bridge between the two _____.

Question 75

Identify the technique that has almost replaced the automated Edman degradation.

A) Gas chromatography
B) Infrared spectroscopy
C) Mass spectroscopy
D) N-terminal Amino acid analysis

Question 76

Disulfide bonds form between the thiol side chains of cysteine. What is the best term to describe the reaction of two thiols to give a disulfide bond?

Question 77

Provide the major organic product of the following reaction that is used in the chemical synthesis of peptides.