Deck 22: Special Topic: Amino Acids and Polyamino Acids Peptides and Proteins

Question 1

Which of the following residues does not appear in RNA?

A)C
B)A
C)G
D)T
E)U

Answer 1

T

Question 2

Which of these structurs is alanine?

A)
B)
C)
D)
E)

Answer 2

Question 3

A sample of a mixture containing lysine, glutamic acid, cysteine, and histidine is placed on a piece of paper moistened with a solution at pH 5.0 . An electrical field is then applied across the paper to separate the amino acids (electrophoresis). Starting from a position closest to the anode and proceeding toward the cathode, what amino acids would be encountered?

A) Glu, Cys, His, Lys
B) Lys, His, Cys, Glu
C) Cys, His, Glu, Lys
D) His, Glu, Cys, Lys
E) Cys, Glu, His, Lys

Answer 3

Glu, Cys, His, Lys

Question 4

What is the name for this peptide?

A) Gly-Leu-Met-Cys
B) Ala-Leu-Met-Cys
C) Ala-Ile-Cys-Met
D) Gly-Ile-Cys-Met
E) Ile-Met-Cys

Question 5

Which statement is true?

A)Kinetic resolution is used to separate diastereomeric amino acids.
B)Optically inactive alkaloids are used to convert two enantiomeric amino acids into two diastereomeric ammonium salts.
C)A racemic mixture of amino acids can be separated by enzymatically modifying either the D- or L-amino acid in such a way that it can be separated from the other.
D)D-amino acids are more prevalent in nature than L-amino acids.
E)A racemic mixture of amino acids can be separated by fractional crystallization.

Question 6

The isoelectric point for an artificial amino acid is 6.2 and the of its carboxyl group is 2.4 . What is the of its ammonium group?

A) 10.0
B) 8.6
C) 3.8
D) 9.4
E) 4.3

Question 7

The first Merrifield machine produced a 125 amino acid peptide with an overall yield of 17%. What was the average yield of each step in this synthesis?

A)83.0%
B)96.8%
C)99.8%
D)98.6%
E)The average yield cannot be determined.

Question 8

Which of these structures correctly shows proline at pH=7 ? The pK_a values for the carboxylic acid and amine group in proline are 2.0 and 10.6 , respectively.

A)
B)
C)
D)
E)

Question 9

Which of these is the correct Fischer projection for L-serine?

A)

B)

C)

D)

E)

Question 10

Given the following information about a polypeptide
Hydrolysis of the polypeptide gives the following amino acids: Arg; Gly; Lys; Met(3) ; Phe(2);
Ser(2) ; Tyr.
Treatment of the polypeptide with chymotrypsin gives the following fragments: Met-Lys-Ser-Phe; Ser-Gly-Tyr; Met-Arg-Phe; Met.
Treatment of the polypeptide with cyanogen bromide gives the following fragments:
Ser-Gly-Tyr-[lactone]; Arg-Phe-[lactone]; Lys-Ser-Phe-[lactone].
Sanger degradation gives 2,4-DNP-Ser.
What is the primary structure of the original polypeptide?

A) Ser-Gly-Tyr-Met-Arg-Phe-Met-Lys-Ser-Phe-Met
B) Lys-Ser-Phe-Met-Ser-Gly-Tyr-Met-Arg-Phe-Met
C) Met-Lys-Ser-Phe-Met-Arg-Phe-Met-Ser-Gly-Tyr
D) Ser-Gly-Tyr-Met-Lys-Ser-Phe-Met-Arg-Met-Phe
E) Ser-Phe-Met-Arg-Phe-Met-Ser-Gly-Tyr-Met-Lys

Question 11

Why does proline not give a positive test with ninhydrin?

A) The secondary amine of proline is too weak a nucleophile to add to ninhydrin.
B) The of the ammonium in proline (10.6) is too high to react with ninhydrin.
C) Hydrolysis of the second imine in the reaction mechanism cannot occur with proline.
D) The first imine cannot form in the reaction between proline and ninhydrin.
E) The second imine formed by decarboxylation in the mechanism is too unstable to form.

Question 12

A certain amino acid has values of 2.35 and 9.6 for its carboxylic acid and amino group, respectively. What is the isoelectric point for this amino acid?

A) 2.35
B) 9.6
C) 6.0
D) 7.25
E) 11.95

Question 13

Which statement is true about aspartic acid at pH 3.0 ? The values are shown in the following figure.

A) There is an overall 1+ charge.
B) There is an overall 1 - charge.
C) The molecule is neutral, and as shown in the figure, there are no nonzero formal charges on any of the atoms in the major resonance contributor.
D) The molecule is a zwitterion.
E) There is an overall 2+ charge.

Question 14

Which of these structures are L-amino acids?

A) I
B) I and II
C) I, II, and III
D) III and IV
E) I and IV

Question 15

Which of the following would you use to protect the amino terminus in a polypeptide synthesis?

A)phenylisothiocyanate
B)2.4-dinitrofluorobenzene
C)DCC
D)BrCN
E)benzylchloroformate

Question 16

Which of the following properties dictate the overall structure of a polypeptide?

A)the sequence of amino acids in the polypeptide chain
B)the presence of disulfide bonds between sulfur containing residues on the chain
C)hydrogen bonding between side chains on peptide residues
D)orientation of hydrophilic groups out and hydrophobic groups in in the structure
E)all these properties impact the overall structure of the polypeptide

Question 17

Denaturation is

A)disruption of the primary structure of a protein.
B)disruption of the secondary structure of a protein.
C)disruption of the tertiary structure of a protein.
D)disruption of the quaternary structure of a protein.
E)all of these.

Question 18

Which steps will be necessary to synthesize the peptide shown here? I.The N-terminus of Ile will require protection. II.The N-terminus of Phe will require protection.
III)The carboxy terminus of Ile will require protection.
IV)The carboxy terminus of Phe will require protection.

A)I and II
B)I and III
C)I and IV
D)II and III
E)I, II, III, and IV

Question 19

α-helix and β-pleated sheets are examples of what type of protein structure?

A)primary
B)secondary
C)tertiary
D)quaternary
E)all of these

Question 20

Which of the following statements about ninhydrin is false?

A)Reaction of an amino acid with ninhydrin results in a decarboxylation.
B)Reaction of ninhydrin with any amino acid eventually produces an imine that appears purple.
C)When an amino acid reacts with ninhydrin, eventually the "R" group is lost from the amino acid.
D)Ninhydrin reacts with amino acids through its carbonyl form, not its hydrated form.
E)The purple molecule that results from reaction of ninhydrin with an amino acid is an imine.

Question 21

Show the mechanism of the first step in the Strecker synthesis to prepare racemic leucine from
3-methylbutanal.

Question 22

Draw the structure of Asp-Gln-Tyr.

Question 23

Explain how kinetic resolution can be used to separate a racemic mixture of D- and L-
phenylalanine.

Question 24

Draw the structure of methionine at pH=5 . Show all nonzero formal charges. The values for methionine are 2.3 for the carboxylic acid and 9.2 for the amino group.

Question 25

Draw the lettered intermediates and product in the following synthesis.

Question 26

Draw a structure for (R)-tyrosine.Show stereochemistry using wedge-and-dash notation.

Question 27

Give the IUPAC name for L-valine.

Question 28

Draw the intermediates and product in the Gabriel synthesis of an amino acid.

Question 29

Draw a Haworth projection of β-2-deoxyribofuranose.The Fischer projection of ribose is shown
for your reference.

Question 30

An 11-amino-acid polypeptide is subjected to the following processes:
Complete hydrolysis of the polypeptide, followed by separation of the component amino acids, shows Gln, Gly, Arg (2), Ala, Cys, Ser, Phe (2), Ile, Val.
Treament with chymotrypsin gives the following peptide chains:
Gln-Arg-Cys-Ala-Ser-Phe; Arg; Gly-Ile-Val-Phe.
Treatment with 2,4-DNP followed by hydrolysis (Sanger degradation) gives 2,4-DNP-Gly.
Treatment with a carbopeptidase removes an arginine (Arg) amino acid from the peptide.
What is the sequence of the amino acids in the original polypeptide?

Question 31

At a pH of 6.0 , indicate whether each amino acid shown would be in cationic, anionic, or zwitterionic form.

Question 32

Outline a synthesis of this peptide using any amino acids and protecting groups necessary.

Question 33

Draw a Fischer projection for L-glutamic acid at pH=6 . The values are: carboxylic acid, 2.2 ; ammonium group, 9.7 ; side chain, 4.3 .

Question 34

Explain how the Merrifield method of synthesizing polypeptides results in very high yields.

Question 35

What is the mRNA fragment that will be generated by this strand of DNA?

Question 36

Provide a name for this peptide using the three-letter code for amino acids.

Question 37

Provide the missing reagents in this synthesis.

Question 38

What polypeptide would be produced from an mRNA fragment with the following sequence of
codons?

Question 39

An octapeptide is subjected to Edman degradation and it is discovered that the amino terminus is
Ser.Treatment of the remaining heptapeptide with BrCN yields a tripeptide
A and a tetrapeptide, B.
The tripeptide A is treated with trypsin, releasing a single residue and a dipeptide.The dipeptide,
on Edman degradation, gives two residues, one of which is not optically active.
The tetrapeptide B is also treated with trypsin, releasing a new tripeptide and a His residue.The
tripeptide from this step is treated with chymotrypsin, resulting in a dipeptide and a single amino
acid.Edman degradation of the dipeptide yields two residues, one of which is Val.
There is no Phe or Trp in the original octapeptide.
Provide a possible sequence of the original octapeptide.