Deck 17: Amino Acids, Peptides, and Proteins

Question 1

Under what condition would phenylalanine exist as follows?

A) at a low pH
B) at a high pH
C) at the pI
D) when pH = pK_a
E) none of these

Answer 1

at a high pH

Question 2

In the dipeptide shown the following segment of the molecule is likely to lie in a single plane:

A)
B)
C)
D)
E)

Answer 2

Question 3

What is the only $\alpha$ -amino acid that does not have a stereogenic carbon?

A) glycine
B) alanine
C) phenylalanine
D) valine
E) leucine

Answer 3

glycine

Question 4

Hydrogen bonds, $\alpha$ -helices, and pleated sheets are structural properties of proteins.

A) primary
B) secondary
C) tertiary
D) quaternary
E) sole

Question 5

Which of the following $\alpha$ -amino acids contains a hydroxyl group?

A) asparagine
B) threonine
C) cysteine
D) isoleucine
E) phenylalanine

Question 6

Which of the following molecules is $\alpha$ -aminopropanoic acid?

A)
B)
C)
D)
E)

Question 7

What is the correct relationship between valylalanine and alanylvaline?

A) enantiomeric pair
B) meso compounds
C) structural isomers
D) geometric isomers
E) racemic mixture

Question 8

What is the name of the following molecule?

A) 3-amino-3-phenylvaleric acid
B) 4-amino-4-methyl-4-phenylbutanoic acid
C) 4-amino-4-phenylpentanoic acid
D) 4-amino-4-phenyl-4-methylbutanoic acid
E) 2-amino-2-phenylbutanoic acid

Question 9

The dipeptides are

A) constitutional isomers.
B) stereoisomers.
C) diastereoisomers.
D) enantiomers.
E) identical.

Question 10

What is the name of the amide bond linking two amino acids?

A) ionic
B) hydrogen
C) glycosidic
D) nonpolar
E) peptide

Question 11

How many different combinations are possible for a tripeptide containing one of each of the following amino acids: Phe, Val, Asp?

A) 2
B) 6
C) 8
D) 10
E) greater than 10

Question 12

Which one of the following represents a tetrapeptide?

A) Val-Ile-Asp-Asp
B) Ala-Ala-Ala-Ala-Val-Val
C) Ala-Ser-Val-Val-Ile
D) Ser-Ser-Ala-Ala-Gly-Gly-Glu-Glu
E) Ser-Ala-Thr-Pro-Leu

Question 13

Which molecule is an $\alpha$ -amino acid?

A)
B)
C)
D)
E)

Question 14

Which of the following $\alpha$ -amino acids contains an imidazole?

A) arginine
B) asparagine
C) aspartic acid
D) histidine
E) tyrosine

Question 15

What is the net charge of isoleucine at its isoelectric point?

A) 0
B) +1
C) +2
D) -1
E) -2

Question 16

In the octapeptide, Cys-Ile-Ser-Asp-Gly-His-Gly-Gly, which is the N-terminal amino acid?

A) Ser
B) Ile
C) Asp
D) Cys
E) Gly

Question 17

To what family of polymers do proteins belong?

A) polyesters
B) polyacids
C) polyamines
D) polyurethanes
E) polyamides

Question 18

How many different combinations are possible for a tetrapeptide containing two glycines (Gly,) one alanine (Ala,) and one phenylalanine (Phe)?

A) 3
B) 6
C) 12
D) 24
E) 36

Question 19

In the octapeptide, Phe-Ile-Ser-Asp-Gly-His-Gly-Tyr, which is the C-terminal amino acid?

A) Ser
B) Phe
C) Tyr
D) His
E) Gly

Question 20

Which of the following amino acids can form disulfide bonds?

A) Gly
B) His
C) Cys
D) Asp
E) Glu

Question 21

Which of the following is Sanger's reagent?

A)
B)
C)
D)
E)

Question 22

The structure of at the isoelectric point is:

A)
B)
C)
D)
E)

Question 23

Based on the pKa's of aspartic acid shown below, what is its approximate isoelectric point?

A) 2
B) 3
C) 5
D) 7
E) 10

Question 24

A useful reagent for detecting amino acids is

A) hydrogen peroxide.
B) Tollens' reagent.
C) ninhydrin.
D) Benedict's reagent.
E) Merrifield's reagent.

Question 25

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

A) Arg-Pro-Pro and Gly-Phe and Ser-Pro-Phe
B) Pro-Pro-Gly and Phe-Ser-Pro-Phe-Arg
C) Arg-Pro-Pro-Gly-Phe and Ser-Pro-Phe
D) Arg-Pro-Pro-Gly-Phe-Ser and Pro-Phe

Question 26

At the isoelectric point, the structure of methionine (2-amino-4-methylthiobutanoic acid) is:

A)
B)
C)
D)
E)

Question 27

What class of compound is produced when leucine reacts with acetyl chloride?

A) ester
B) amide
C) ether
D) phenol
E) alcohol

Question 28

Which reagent is used to determine the N-terminal amino acid of a peptide?

A) Jones'
B) Fehling's
C) Ninhydrin
D) Sanger's
E) Tollens'

Question 29

What fragments will be obtained by a trypsin hydrolysis of the following octapeptide? Ala-Val-Trp-Lys-Phe-Gly-Arg-Met

A) Ala-Val-Trp-Lys-Phe and Gly-Arg-Met
B) Ala-Val-Trp-Lys-Phe -Gly and Arg-Met
C) Ala-Val-Trp-Lys and Phe-Gly-Arg and Met
D) Ala-Val-Trp-Lys and Phe and Gly-Arg and Met
E) Ala-Val-Trp and Lys-Phe-Gly and Arg-Met

Question 30

Which of the following will migrate toward the positive electrode in an electrophoresis experiment?

A) I
B) II
C) III
D) I and III
E) none will migrate

Question 31

If an amino acid has one carboxyl group and one amino group, and the pKa's are 2.4 and 9.8 respectively, what is its isoelectric point?

A) 3.7
B) 6.1
C) 7.0
D) 7.9
E) 12.2

Question 32

Sanger's reagent is used

A) to determine the amino acid sequence of a peptide.
B) to determine the C-terminal amino acid of a peptide.
C) to determine the isoelectric point of a peptide.
D) to determine the number of amino acids in a peptide.
E) to determine the N-terminal amino acid of a peptide.

Question 33

Based on the equilibria shown below, what is the net charge on structure IV?

A) -2
B) -1
C) 0
D) +1
E) +2

Question 34

Which reagent is used specifically to cleave the C-terminal amino acid of a peptide?

A) trypsin
B) carboxypeptidase
C) cyanogen bromide
D) chymotrypsin
E) HCl/H₂O

Question 35

The Edman degradation is used

A) to identify the C-terminal amino acid of a peptide.
B) to determine the tertiary structure of peptides.
C) to synthesize peptides.
D) to cleave polypeptides on the carboxyl side of Phe, Tyr, and Trp residues.
E) to identify the N-terminal amino acid of a peptide.

Question 36

Ninhydrin is used

A) to determine the N-terminal amino acid of a peptide.
B) to sequence amino acids in a peptide.
C) to detect amino acids derived from hydrolysis of a peptide.
D) to couple amino acids during solid-phase peptide synthesis.
E) to hydrolyze peptides on the carboxyl side of aromatic amino acid residues.

Question 37

The isoelectric pH (pI) of is likely to be at a pH that is

A) below pK₁.
B) at pK₁.
C) between pK₁ and pK₂.
D) at pK₂.
E) above pK₂.

Question 38

What is the structure of the phenylhydantoin derived from the first cycle of the Edman degradation of Phe-Ala-Ser?

A)
B)
C)
D)
E)

Question 39

A tetrapeptide contains the amino acids Phe, Ala, Gly, and Leu.Partial hydrolysis affords the dipeptides Phe-Ala, Ala-Gly, and Leu-Phe.The structure of the tetrapeptide is

A) Ala-Gly-Leu-Phe.
B) Leu-Phe-Ala-Gly.
C) Gly-Ala-Phe-Leu.
D) Leu-Phe-Gly-Ala.
E) Phe-Leu-Gly-Ala.

Question 40

The mechanism by which Sanger's reagent reacts with an amine is

A) nucleophilic aromatic substitution.
B) electrophilic aromatic substitution.
C) hydrolysis.
D) nucleophilic acyl substitution.
E) electrophilic addition.

Question 41

The reaction of with bromine water is likely to give:

A)
B)
C)
D)
E)

Question 42

Sanger's reagent (2,4-dinitrofluorobenzene) reacts with the following to give, after complete hydrolysis,

A) no labeled amino acids.
B) one labeled and two unlabeled amino acids.
C) one labeled and three unlabeled amino acids.
D) two labeled and one unlabeled amino acids.
E) two labeled and two unlabeled amino acids.

Question 43

The product from the following is:

A)
B)
C)
D)
E)

Question 44

Treatment of with HF (Merrifield method) gives:

A)
B)
C)
D)
E)

Question 45

Which of the following reagents is used to protect the N-terminal amino acid in a solid phase peptide synthesis?

A)
B)
C)
D)
E)

Question 46

Dicyclohexylcarbodiimide (DCC) is used

A) to determine the N-terminal amino acid of a peptide.
B) to sequence amino acids in a peptide.
C) to detect amino acids derived from hydrolysis of a peptide.
D) to couple amino acids during solid-phase peptide synthesis.
E) to hydrolyze peptides on the carboxyl side of aromatic amino acid residues.

Question 47

An aniline derivative that is suitable for use in the Merrifield peptide synthesis is:

A) 1
B) 2
C) 3
D) 4
E) none of the above