Deck 24: Amino Acids and Proteins

Question 1

Which amino acid would have its isoelectric point near pH 10?

A) I
B) II
C) III
D) IV
E) V

Answer 1

I

Question 2

What is the pI of the following amino acid?

A) 12
B) 3.6
C) 4.8
D) 6.0
E) 7.2

Answer 2

6.0

Question 3

What might be concluded upon determining that an unknown amino acid has its isoelectric point near pH 10?

A) It must have a hydrophobic side chain
B) It must have a hydrophilic side chain
C) Its side chain must contain more basic groups then acidic functions
D) Its side chain must contain an acidic group
E) None of the above is a valid conclusion

Answer 3

Its side chain must contain more basic groups then acidic functions

Question 4

Which amino acid is achiral?

A) I
B) II
C) III
D) IV
E) V

Question 5

Disulfide bonds in proteins:

A) result from an oxidation of thiols.
B) help to maintain the shape of proteins.
C) can be broken by reduction.
D) can link two cysteine amino acid residues.
E) All of the above

Question 6

Which amino acid would have its isoelectric point near pH 10?

A) Glycine
B) Tryptophan
C) Serine
D) Proline
E) Lysine

Question 7

Which amino acid is unlikely to be found in a natural protein?

A) I
B) II
C) III
D) IV
E) V

Question 8

Which amino acid would not have its isoelectric point in the pH range 5-7?

A) Leucine
B) Threonine
C) Methionine
D) Arginine
E) Cysteine

Question 9

Which of these amino acids cannot be described as an L amino acid?

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

Question 10

What is the pI of the following amino acid?

A) 1.5
B) 6.3
C) 5.6
D) 9.8
E) 6.8

Question 11

Which amino acid would have its isoelectric point near pH 3?

A) I
B) II
C) III
D) IV
E) V

Question 12

What might be concluded upon determining that an unknown amino acid has its isoelectric point near pH 3?

A) It must have a hydrophobic side chain
B) It must have a hydrophilic side chain
C) Its side chain must contain a basic group
D) Its side chain must contain more acidic groups then basic groups
E) None of the above is a valid conclusion

Question 13

Which amino acid would not have its isoelectric point in the pH range 5-7?

A) Glycine
B) Proline
C) Cysteine
D) Glutamine
E) All of these amino acids have isoelectric point in the pH range 5-7

Question 14

The pH at which the concentration of the dipolar ion (zwitterion)form of an amino acid is at a maximum and the cationic and anionic forms are at equal concentrations is termed the

A) end point.
B) equivalence point.
C) neutral point.
D) isoelectric point.
E) dipolar point.

Question 15

Which of these amino acids is an R amino acid?

A) II and IV
B) IV and V
C) I and III
D) V
E) All of these are R amino acids

Question 16

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

A) I
B) II
C) III
D) IV
E) V

Question 17

Which of these amino acids has the R configuration at the stereogenic center but,nonetheless,is an L amino acid?

A) I
B) II
C) III
D) IV
E) V

Question 18

Which amino acid would have its isoelectric point near pH 10?

A) I
B) II
C) III
D) IV
E) V

Question 19

What is the pI of the following amino acid?

A) 1.6
B) 3.2
C) 5.5
D) 6.2
E) 7.0

Question 20

Which of these amino acids is a D amino acid?

A) I
B) II
C) III
D) IV
E) V

Question 21

Which of these amino acids is described as an "essential" amino acid?

A) Methionine
B) Phenylalanine
C) Isoleucine
D) Tryptophan
E) All of these are "essential" amino acids

Question 22

Which of these natural amino acids contains a heterocyclic ring?

A) Asparagine
B) Proline
C) Arginine
D) Histidine
E) B and D

Question 23

Which of these natural amino acids contains an -OH group?

A) Serine
B) Threonine
C) Tyrosine
D) Two of these
E) All of these

Question 24

Pipecolic acid logically would be substituted for which natural amino acid in the synthesis of peptide analogs?

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

Question 25

Which of these natural amino acids contains two carboxylic acid groups?

A) Cystine
B) Cysteine
C) Glutamic acid
D) A and B
E) A and C

Question 26

Which is an isolable intermediate in the Strecker synthesis of an amino acid?

A) I
B) II
C) III
D) IV
E) V

Question 27

Which of these natural amino acids,when present in a polypeptide,is likely to exhibit significant hydrogen bonding through its side chain?

A) Serine
B) Threonine
C) Tyrosine
D) Two of these
E) All of these

Question 28

Which of these amino acids is formed from a precursor amino acid only after the latter has been incorporated into a polypeptide chain?

A) Serine
B) Arginine
C) Isoleucine
D) Tryptophan
E) Hydroxyproline

Question 29

What would be the predominant form of lysine in water at pH 14?

A) I
B) II
C) III
D) IV
E) V

Question 30

Which of these natural amino acids contains an indole ring?

A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) 4-Hydroxyproline
E) Asparigine

Question 31

Which of these natural amino acids contains an amide function?

A) Asparagine
B) Methionine
C) Cysteine
D) Glutamine
E) Two of these

Question 32

Which of these natural amino acids,when present in a polypeptide,is not likely to exhibit significant hydrogen bonding through its side chain?

A) Leucine
B) Threonine
C) Tyrosine
D) Serine
E) All of these are likely to exhibit significant hydrogen bonding through the side chain

Question 33

Which of these natural amino acids contains an imidazole ring?

A) Histidine
B) Lysine
C) Tryptophan
D) 4-Hydroxyproline
E) Two of the above

Question 34

Which of these natural amino acids contains a pyrrolidine ring?

A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) 4-Hydroxyproline
E) Serine

Question 35

Which of these amino acids is described as an "essential" amino acid?

A) Threonine
B) Glycine
C) Tyrosine
D) Serine
E) All of these are "essential" amino acids

Question 36

Which of these amino acids contains a hydrophobic side chain?

A) Lysine
B) Serine
C) Methionine
D) Arginine
E) Cysteine

Question 37

For the accompanying fully-protonated amino acid,what is the arrangement of pK_a values in order of increasing magnitude?

A) I < II < III
B) II < I < III
C) III < I < II
D) III < II < I
E) II < III < I

Question 38

Which of these natural amino acids contains a phenolic group?

A) Phenylalanine
B) Tyrosine
C) Tryptophan
D) 4-Hydroxyproline
E) Serine

Question 39

Which of these natural amino acids contains an amide function?

A) Asparagine
B) Proline
C) Arginine
D) Histidine
E) None of these

Question 40

The predominant form of aspartic acid in water at pH 1 would be:

A) I
B) II
C) III
D) IV
E) V

Question 41

What product(s)would you expect from the following reaction?

A) I
B) II
C) III
D) IV
E) V

Question 42

The Edman degradation uses this reagent to identify the N-terminal amino acid of a peptide or protein.

A) C₆H₅NHNH₂
B) C₆H₅NH₂
C) C₆H₅N=C=S
D) C₆H₅N=C=O
E) Aminopeptidase

Question 43

How many different tripeptides can exist,each containing one residue of glycine,one of L-threonine,and one of L-arginine?

A) 2
B) 3
C) 6
D) 8
E) 9

Question 44

The purple color of the anion formed in the ninhydrin test for α-amino acids is due to:

A) the attraction of the anion to a metal in a pi-complex.
B) intermolecular hydrogen bonding.
C) molecular vibrations.
D) the highly conjugated nature of the anion.
E) the color of the ninhydrin.

Question 45

Which amino acid of a polypeptide would become labeled when the polypeptide is treated with 2,4-dinitrofluorobenzene in base,even though the amino acid is not a terminal amino acid?

A) Lysine
B) Glycine
C) Alanine
D) Phenylalanine
E) Leucine

Question 46

Why is this sequence,CH₂=CHCH₂OH + HBr,then CrO₃/H₂SO₄/H₂O,finally xs NH₃,not a good method for the preparation of L-alanine?

A) NH₃ is not sufficiently nucleophilic to perform the final step.
B) HBr does not add to substituted alkenes.
C) 1° alcohols are not oxidized by CrO₃ in acidic solution.
D) Initial HBr addition produces a racemic intermediate which leads to racemic product.
E) Steric hindrance precludes nucleophilic substitution at a 2° carbon atom.

Question 47

When the pentapeptide below is heated first with 2,4-dinitrofluorobenzene (and base)and then subjected to acidic hydrolysis,which amino acid will bear the dinitrophenyl group? Leu·Val·Gly·Phe·Ile

A) Leucine
B) Valine
C) Glycine
D) Phenylalanine
E) Isoleucine

Question 48

A pentapeptide has the molecular formula: Asp,Glu,His,Phe,Val.Partial hydrolysis of the pentapeptide gives: Val·Asp,Glu·His,Phe·Val,and Asp·Glu.What is the amino acid sequence of the pentapeptide?

A) Phe·Val·Asp·Glu·His
B) His·Glu·Asp·Val·Phe
C) Asp·Glu·His·Phe·Val
D) Phe·Val·Glu·His·Asp
E) Glu·His·Phe·Val·Asp

Question 49

Predict the direction of migration (toward anode or cathode)of alanine during electrophoresis at pH = 5.

Question 50

Why is dicyclohexylcarbodiimide (DCC)used in peptide synthesis?

A) DCC "protects" the amino group of the intended N-terminal amino acid.
B) DCC activates the carboxyl group of one amino acid so that this amino acid reacts more readily with a second amino acid.
C) DCC cleaves the blocking groups from the final peptide.
D) DCC is the resin used in the automated synthesis of peptides.
E) DCC removes the peptide from the resin at the conclusion of the synthesis.

Question 51

The primary structure of a protein refers to its:

A) sequence of amino acid residues.
B) disulfide bonds.
C) helical structure.
D) hydrogen bonding.
E) All of these

Question 52

Which of these is used to convert a protein into smaller,more manageable fragments for subsequent structural studies?

A) Insulin
B) Aminopeptidase
C) Carboxypeptidase
D) Trypsin which is produced in the HYPERLINK "http://en.wikipedia.org/wiki/Pancreas" \o "Pancreas" pancreas as the inactive HYPERLINK "http://en.wikipedia.org/wiki/Proenzyme" \o "Proenzyme" proenzyme HYPERLINK "http://en.wikipedia.org/wiki/Trypsinogen" \o "Trypsinogen" trypsinogen.
E) 2,4-Dinitrofluorobenzene

Question 53

The occurrence of this amino acid in a polypeptide chain disrupts an α-helix:

A) Proline
B) Alanine
C) Methionine
D) Histidine
E) Tyrosine

Question 54

This reagent is used to "protect" the amino group of an amino acid which is to be joined to a second amino acid by a peptide bond.

A)

B)

C)

D)

E)

Question 55

What product would be obtained upon treating alanine with the following reagent ?

A) I
B) II
C) III
D) IV
E) V

Question 56

The secondary structure of proteins is derived from:

A) peptide linkages.
B) disulfide linkages.
C) hydrogen bond formation.
D) hydrophobic interactions.
E) acid-base interactions.

Question 57

A "conjugated protein" is one which:

A) possesses catalytic properties.
B) is a digestive enzyme.
C) exists largely as an α-helix.
D) contains unsaturated amino acids.
E) contains a nonprotein group as part of the molecule.

Question 58

Which one of these amino acids does not give the usual purple color with ninhydrin?

A) Histidine
B) Proline
C) Tryptophan
D) Leucine
E) Aspartic acid

Question 59

A heptapeptide Ala₂,Glu,Phe,Pro,Tyr,Val gives labeled alanine when heated with DNFB followed by hydrolysis.On partial hydrolysis the unlabeled heptapeptide gives the following: Ala·Glu,Pro·Tyr,Ala·Val,Tyr·Ala,Val·Phe·Pro.
What is the amino acid sequence of the heptapeptide?

A) Ala·Phe·Pro·Tyr·Ala·Glu·Val
B) Ala·Val·Phe·Pro·Tyr·Ala·Glu
C) Ala·Val·Phe·Pro·Tyr·Glu·Ala
D) Ala·Val·Phe·Tyr·Pro·Ala·Glu
E) Val·Ala·Phe·Tyr·Pro·Ala·Glu

Question 60

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

A) Disulfide linkages
B) Hydrogen bonds
C) van der Waals forces
D) Hydrophobic interactions
E) All of these

Question 61

Give the structure of the aldehyde which,upon treatment with HCN and ammonia,followed by heating with aqueous acid,would afford racemic tryptophan.What is this strategy for the synthesis of $\alpha$ -amino acids called?

Question 62

Peptide synthesis has four basic steps.These are:

Question 63

Beginning with a three-carbon alcohol,outline all necessary steps in the preparation of D,L-alanine.

Question 64

Complete the following equations:

Question 65

Amino acids can be prepared from aldehydes by treatment with ammonia and HCN followed by hydrolysis.This method is known as the ___________.

Question 66

What is the final product formed when potassium phthalimide is subjected to the following reaction sequence? Give structural details of all significant intermediates,including stereochemistry,as applicable.

Question 67

Complete the reaction presented below:

Question 68

The amino acid threonine, (2S,3R)-2-amino-3-hydroxybutanoic acid,has two chiral
centers.Draw a Fisher projection of threonine.

Question 69

The pH at which the concentration of the zwitterionic form (dipolar form)of an amino acid is at its highest and the concentrations of the cationic and anionic forms are equal is called the _____________.

Question 70

Draw the structures of ValAla and AlaVal as zwitterions.

Question 71

Draw the structures of the predominant forms of glycine at pH = 2.0,6.0,and 10.Indicate the direction of migration (toward anode or cathode)for each structure.

Question 72

Draw the Fisher projection of a threonine diastereomer,and label the chiral centers as R
or S.

Question 73

A reagent that reacts with most amino acids to give an intense purple color is called ___________.

Question 74

Draw the structure of L-phenylalanine and L-valine in Fischer projection.

Question 75

The 22 $\alpha$ -amino acids can be subdivided into three different types on the basis of the structures of their side chains.These three types are: ____________.

Question 76

Show how a Strecker synthesis might be used to prepare phenylalanine starting from phenylacetldehyde.

Question 77

Using the three-letter code names for amino acids,write the structures of all possible peptides containing these amino acids: Val,Ser,Leu

Question 78

What is the final product formed via the following reaction sequence? Give structural details of all significant intermediates.

Question 79

What are the name and the structure of the products A and B?

Question 80

The Henderson-Hasselbach equation shows that the ________________ of an acid is the ________________ at which the acid is half-neutralized.