Deck 26: Amino Acids,peptides,proteins,and Nucleic Acids: Nitrogen-Containing Polymers in Nature

Question 1

Which of the following is least likely to be found in nature?

A)

B)

C)

D)

E)

Answer 1

Question 2

Which of the following amino acids would have the highest isoelectric point?

A) Lysine
B) Glutamine
C) Aspartic acid
D) Alanine
E) Tryptophan

Answer 2

Lysine

Question 3

Why is the following not a good two step route for the preparation of pure L-alanine?

A) The bromination is not selective (the CH₃ and CH₂ groups are both brominated).
B) Ammonia is not sufficiently nucleophillic to react with a secondary bromide.
C) Only the CH₃ group is brominated.
D) The product will be racemic.
E) Propanamide would be the major product.

Answer 3

The product will be racemic.

Question 4

Disulfide bonds in proteins

A) result from oxidation of thiols (RSH).
B) function to help maintain the shape of proteins.
C) can be broken by reduction reactions.
D) link two cysteine amino acid residues.
E) All of these are true.

Question 5

Why is the additional (ring)nitrogen in tryptophan not very basic?

A) Cyclic amines are not basic.
B) It is too far from the carboxyl group to be effected.
C) Aromatic amines are weakly basic because of resonance.
D) The additional amine group is offset by an additional carboxylic acid group.
E) It is sp² hybridized as therefore not as basic.

Question 6

The primary structure of a protein refers to the

A) sequence of amino acids.
B) overall 3-dimensional shape.
C) localized shape of the backbone.
D) degree of aggregation with other proteins.
E) structure of the active site.

Question 7

What material can be used repetitively (on a given sample)to sequence a polypeptide from the N-terminal end?

A) Chymotrypsin
B) Sanger reagent
C) Trypsin
D) Edman reagent
E) Carboxypeptidase

Question 8

Nearly all amino acids immediately release N₂ gas upon diazotization (treatment with aqueous HCl and sodium nitrite).Which amino acid would not?

A) Lysine
B) Histidine
C) Tyrosine
D) Cysteine
E) Proline

Question 9

Which of the following amino acids is theoretically capable of existing in two diastereomeric forms?

A) Cysteine
B) Threonine
C) Leucine
D) Serine
E) Tryptophan

Question 10

What is dicyclohexylcarbodiimide (DCC)used for in peptide synthesis?

A) DCC protects the amino group of the intended N-terminal amino acid.
B) DCC activates the carboxyl group toward nucleophillic attack.
C) DCC cleaves the blocking groups from the final peptide.
D) DCC is the resin (solid support)used to anchor the growing polypeptide.
E) DCC removes the peptide from the resin at the conclusion of the synthesis.

Question 11

What is the name of the DNA base shown?

A) Guanine
B) Cytosine
C) Adenine
D) Uracil
E) Thymine

Question 12

What would be the abbreviated name of the following polypeptide?

A) val-thr-glu-ala-gln
B) ala-thr-glu-val-gln
C) met-ser-asp-leu-pro-NH₂
D) ala-ser-asp-val-gln
E) ala-ser-asp-val-pro-NH₂

Question 13

Which amino acid does not have an enantiomer?

A) Alanine
B) Glutamine
C) Histidine
D) Aspartic acid
E) Glycine

Question 14

How many tripeptides containing one residue each of L-alanine,L-valine,and glycine are possible?

A) 2
B) 3
C) 4
D) 6
E) 9

Question 15

In a DNA molecule,at which point would the base shown be attached to a deoxyribose fragment?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 16

Chymotrypsin catalyzes hydrolysis of peptide bonds where?

A) At the carboxy end of residues with basic side chains
B) At the amino end of residues containing aliphatic residues
C) At the carboxy end of residues with aromatic side chains
D) At the amino end of residues with aromatic side chains
E) At the carboxy end of methionine residues

Question 17

The artificial sweetener aspartame is a derivative of the dipeptide asp-phe.If aspartame (asp-phe)was prepared from racemic amino acids,how many stereoisomers (diastereomers + enantiomers)could be formed?

A) 2
B) 3
C) 4
D) 6
E) 8

Question 18

How many amino acid residues are present in the following polypeptide?

A) 4
B) 5
C) 6
D) 7
E) 8

Question 19

Which amino acid does not form a characteristic blue color with ninhydrin?

A) Cysteine
B) Lysine
C) Proline
D) Valine
E) Tryptophan

Question 20

It was not until 1974 that $\gamma$ -carboxyglutamic acid (shown below)was discovered (by researchers at the University of Colorado)in polypeptides.Based on your knowledge of organic chemistry,what is the most likely reason that this particular amino acid escaped identification so long?

A) It tended to spontaneously form a cyclic anhydride:

B) It tended to spontaneously lose carbon dioxide:

C) It easily underwent a reverse-Knovenagle reaction:

D) It tended to spontaneously form a cyclic amide (lactam):

E) It was simply too polar to extract into non-polar organic solvents.

Question 21

The secondary structure of proteins is held together by hydrogen bonds between which protein sub-structures?

A) The C=O and N-H on amino acid side chains
B) The C=O on the protein backbone and the N-H on the amino acid side chains
C) The C=O on the amino acid side chains and the N-H on the protein backbone
D) The C=O and the N-H on the protein backbone
E) There are no hydrogen bonds involved with secondary structure.

Question 22

Which amino acid is shown?

A) Alanine
B) Glycine
C) Tyrosine
D) Lysine
E) Arginine

Question 23

Which of the following DNA base pairs can participate in Watson and Crick type hydrogen bonding?

A) A-T
B) G-T
C) G-C
D) Both A and B
E) Both A and C

Question 24

Which attractive force is responsible for maintaining the tertiary structure of proteins?

A) Disulfide linkages
B) Hydrogen bonds
C) Salt bridges
D) Hydrophobic interactions
E) All of these

Question 25

The difference(s)between DNA and RNA is (are):

A) DNA incorporates 2-deoxyribose sugars rather than ribose.
B) RNA is smaller than DNA.
C) DNA uses thymine,RNA uses uracil.
D) Two of the above are true.
E) All of the above are true.

Question 26

At the isoelectric point,the amino acid alanine will exist as what structure?

A) A positive ion
B) A negative ion
C) An uncharged molecule
D) A zwitterion
E) A carbocation

Question 27

Which of the following amino acids contains an aromatic ring?

A) Alanine
B) Serine
C) Tyrosine
D) Asparagine
E) Glycine

Question 28

Which amino acid is responsible for the condition known as phenylketonuria (PKU)which occurs in a small fraction of the population?

A) Tryptophan
B) Histidine
C) Phenylalanine
D) Proline
E) Valine

Question 29

What process would one use to make multiple copies of a fragment of DNA?

A) Polymerase chain reaction
B) Electrophoresis
C) Transcription
D) Translation
E) Merrifield solid-phase synthesis

Question 30

Amino acids are covalently bonded to each other through_______.

A) hydrogen bonding
B) disulfide bridges
C) peptide bonds
D) ( $\alpha$ and $\beta$ folds)
E) None of the above.

Question 31

The organic portion of which of the following biological materials does not consist mainly of polypeptides and/or proteins?

A) Enzymes
B) Hair
C) Hemoglobin
D) Membranes
E) Insulin

Question 32

Although traces of racemic amino acids have been found in meteorites,nearly all naturally occurring amino acids on Earth have the stereochemistry shown.What is true of this stereochemistry? (Assume R = alkyl)

A) Amino acids are of the (R)configuration.
B) Amino acids are of the (S)configuration.
C) Amino acids are not chiral.
D) Amino acids are meso compounds.
E) Amino acids easily change configuration.

Question 33

Folding of polypeptides influenced by distant residues is an example of what protein structure?

A) Primary
B) Secondary
C) Tertiary
D) Quaternary
E) None of the above.

Question 34

Which of the following represents how a typical amino acid would mainly exist in basic solution (pH > 7)?

A)

B)

C)

D)

E) None of the above.

Question 35

How many polypeptides would be present if the following was treated with trypsin?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 36

Which nitrogen in the imidazole ring of histidine is the more basic?

A) #1
B) #2
C) both have same basicity
D) neither is basic
E) the histidine N-H is actually acidic

Question 37

Which of the following statements is not true of amino acids?

A) They are less acidic than carboxylic acids.
B) In acid solution (pH ~ 2)they would show an IR absorption near 1720 cm^-1_.
C) They are soluble in water but not in non-polar organic solvents.
D) They are more basic than amines.
E) In basic solution (pH ~ 12)they would show an IR absorption near 3300 cm^-1_.

Question 38

What would result from the following reactions?

A)

B)

C)

D)

E)

Question 39

Given that the pK_a of the acidic form of proline is 2.0,and the pK_a of the basic form of proline is 10.6,what is the isoelectric point?

A) 2.0
B) 6.3
C) 4.4
D) 10.6
E) 7.0