Deck 21: Amino Acids,peptides,and Proteins

Question 1

Which of the following amino acids has an aromatic R group?

A)serine
B)cysteine
C)asparagine
D)tyrosine
E)leucine

Answer 1

tyrosine

Question 2

Provide the Fischer projection of L-aspartic acid.

Answer 2

Question 3

Explain what essential amino acids are and list all of them.

Answer 3

An essential amino acid is one that humans must obtain from their diet because it cannot be synthesized at all or in sufficient quantity in the body.They are valine,leucine,isoleucine,threonine,methionine,lysine,arginine,phenylalanine,histidine,and tryptophan.

Question 4

Draw the form of L-tryptophan which is present at biological pH.

Question 5

Name the following compound.

A)tyrosine
B)lysine
C)arginine
D)histidine
E)phenylalanine

Question 6

Draw and name the amino acids which may be described as heterocyclic.

Question 7

Name the following compound.

A)cysteine
B)threonine
C)methionine
D)serine
E)asparagine

Question 8

Which of the following amino acids is not an aromatic compound?

A)phenylalanine
B)threonine
C)histidine
D)tryptophan
E)tyrosine

Question 9

Which of the following terms best describes the side chain of valine?

A)acidic
B)basic
C)charged,polar
D)uncharged,polar
E)nonpolar

Question 10

Which of the following amino acids has a sulfur in the R group?

A)serine
B)cysteine
C)asparagine
D)tyrosine
E)leucine

Question 11

Draw glutamate.

Question 12

Which of the following amino acids has an aliphatic R group?

A)serine
B)cysteine
C)asparagine
D)tyrosine
E)leucine

Question 13

In nature,which is the most commonly found isomer,L-amino acids or D-amino acids?

Question 14

Name the following compound.

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

Question 15

Which of the following amino acids has a heterocyclic R group?

A)glycine
B)threonine
C)proline
D)aspartic acid
E)arginine

Question 16

What is the net charge of arginine in a solution of pH 1.0?

Question 17

Which of the following molecules is the skeletal structure of an amino acid?

A)
B)
C)
D)
E)

Question 18

Which of the following is an L-amino acid?

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

Question 19

The α-carbon of all the amino acids is a chirality center except for

A)glycine
B)threonine
C)proline
D)aspartic acid
E)arginine

Question 20

Draw the form of L-lysine which is present at biological pH.

Question 21

Which of the following amino acids will be closest to the origin when separated by thin-layer chromatography?

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

Question 22

Which of the following amino acids will be retained longest in the column when separated by cation-exchange chromatography?

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

Question 23

What is the pI of arginine? The structure and pKa values are shown below.

A)10.76
B)7)90
C)5)61
D)7)33
E)9)67

Question 24

Which of the following amino acids has a side chain with an ionizable proton and can exist in four different forms,depending on the pH of the solution?

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

Question 25

Draw structures for the forms of glycine present in basic,neutral,and acidic solutions.

Question 26

What is electrophoresis?

A)a technique that separates amino acids on the basis of their polarity
B)a technique that separates amino acids on the basis of their solubility in water
C)a technique that separates amino acids on the basis of their pI values
D)a technique that separates amino acids on the basis of pKa of α-COOH values
E)a technique that separates amino acids on the basis of pKa of α-⁺NH₃ values

Question 27

Calculate the isoelectric point for the following compound.

A)3)22
B)5)34
C)5)93
D)6)91
E)9)67

Question 28

Draw the form in which glutamate exists at pH = 0.

Question 29

What is thin-layer chromatography?

A)a technique that separates amino acids on the basis of their polarity
B)a technique that separates amino acids on the basis of their solubility in water
C)a technique that separates amino acids on the basis of their pI values
D)a technique that separates amino acids on the basis of pKa of α-COOH values
E)a technique that separates amino acids on the basis of pKa of α-⁺NH₃ values

Question 30

Which of the following amino acids has the highest isoelectric point?

A)arginine
B)aspartic acid
C)glycine
D)proline
E)phenylalanine

Question 31

Draw the predominant form of aspartate at physiological pH.

Question 32

Which of the following best represents the structure of an amino acid in basic solution (pH = 11)?

A)
B)
C)
D)
E)

Question 33

Which of the following best describes the side chain of arginine at a pH of 11?

A)hydrophobic
B)nonpolar
C)charged and polar
D)uncharged but polar
E)aprotic

Question 34

Which of the following is a zwitterion?

A)
B)
C)
D)
E)

Question 35

Draw the predominant form of histidine at pH=0.

Question 36

Draw the predominant form of proline at pH=12.

Question 37

Define what is meant by isoelectric point (pI)and give an example.

Question 38

Which of the following amino acids has its isoelectric point at the lowest pH?

A)glutamic acid
B)lysine
C)valine
D)glycine
E)methionine

Question 39

What is the pI of glycine? The structure and pKa values are shown below.

A)7)26
B)5)97
C)3)63
D)7)50
E)11.94

Question 40

Give the pH at which histidine exists in the following form.

A)0
B)4
C)8
D)12
E)14

Question 41

What amino acid can be obtained by the reductive amination of γ-ketoglutaric acid,HO₂CCH₂CH₂COCO₂H?

A)glycine
B)serine
C)lysine
D)aspartic acid
E)glutamic acid

Question 42

What is the product obtained from the mild oxidation of the thiol shown below?

A)R-S-R
B)R-OH
C)R-S-S-R
D)R-OO-R
E)R-S-OH

Question 43

Give the product for the following reaction.

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

Question 44

What is an amino acid analyzer?

Question 45

What is the name of the amino acid produced when propanoic acid is subjected to the following sequence of reagents? 1.PBr₃,Br₂
2)H₂O
3)NH₃,Δ

A)alanine
B)aspartic acid
C)glutamic acid
D)valine
E)asparagine

Question 46

Give the product for the following reaction.

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

Question 47

Give the product for the following reaction.

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

Question 48

Which labeled bond in the following molecule is known as the peptide bond?

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

Question 49

Rank the following amino acids in order of time of elution from a cation-exchange resin and a buffer pH of 4.0: aspartic acid,phenylalanine,arginine,and alanine.

Question 50

Give the product for the following reaction.

Question 51

Give the product for the following reaction.

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

Question 52

Explain what is meant by kinetic resolution and give an example.

Question 53

Provide the major organic product(s)of the reaction below.

Question 54

What is the major organic product of the following reaction?

A)
B)
C)
D)
E)

Question 55

Provide the major organic product(s)of the reaction below.

Question 56

Provide the major organic product(s)of the reaction below.

Question 57

Rate the following amino acids in decreasing order of migration towards the cathode (negative electrode)when separated by electrophoresis in a solution of pH= 7.3.
I.lysine: pI= 9.87
II.alanine: pI= 6.02
III.aspartate: pI= 5.95

Question 58

You are given a mixture that contains glutamic acid (pI = 3.2),arginine (pI = 10.8),and valine (pI = 6.0),and you subject the mixture to electrophoresis.
a)Which amino acids migrate toward the cathode when the electrophoresis is carried out at a pH of 7.1?
b)Which amino acids migrate toward the anode when the electrophoresis is carried out at a pH of 7.1?
c)Which amino acid migrates farthest toward the anode at a pH of 7.1?
d)Since amino acids themselves are colorless,how is the separation of amino acids after electrophoresis detected?

Question 59

Which of the following is an acceptable name for the peptide sequence shown below? Glu-Glu-His-Val-Cys

A)1,2-diglutamylhistidylvalylcysteine
B)glutamylglutamylhistidylvalylcysteine
C)1-glutamyl-2-glutamylhistidylvalylcysteine
D)diglutamylhistidylvalylcysteine
E)biglutamylhistidylvalylcysteine

Question 60

Describe how electrophoresis works.

Question 61

Provide the structure of the tripeptide val-gly-ser at pH 12.

Question 62

Provide the structure of the tripeptide glu-ser-ala at pH 12.

Question 63

Give a detailed,stepwise mechanism for the formation of the activated acyl derivative from the reaction of an amino acid with N,N'-dicyclohexylcarbodiimide.

Question 64

Provide the structure of Thr-Gln-Met at pH 7.0.

Question 65

Draw the dipeptide Val-Tyr at pH 7.0.

Question 66

In peptide synthesis,give the use of di-tert-butyl dicarbonate.

A)activates the carboxyl group of an amino acid
B)protects the carboxyl group of an amino acid
C)protects the amino group of an amino acid
D)activates the amino group of an amino acid
E)removes the protecting group on the N-terminal amino acid

Question 67

Explain the importance of the Merrifield method in peptide synthesis.

Question 68

In peptide synthesis,give the use of trifluoroacetic acid.

A)activates the carboxyl group of an amino acid
B)protects the carboxyl group of an amino acid
C)protects the amino group of an amino acid
D)activates the amino group of an amino acid
E)removes the protecting group on the N-terminal amino acid

Question 69

Provide the structure of the tripeptide val-gly-ser at pH 2.

Question 70

Which of the following structures can polypeptides have?

A)primary structure
B)secondary structure
C)tertiary structure
D)quaternary structure
E)all of the above

Question 71

Draw the structure of the tetrapeptide Ser-Leu-Phe-Pro at pH 7.0.

Question 72

In conventional peptide synthesis,the nitrogen of a given amino acid must be deactivated or blocked while the carboxyl group is activated.Which of the following reagents is used to protect the amino group of an amino acid?

A)di-tert-butyl dicarbonate
B)dicyclohexylcarbodiimide
C)ninhydrin
D)trifluoroacetic acid
E)phenylisothiocyanate

Question 73

Which type of protein,globular or fibrous,tends to function primarily as structural parts of an organism?

Question 74

Give the product for the following reaction.

A)
B)
C)
D)
E)

Question 75

Provide the structure of Ala-Ser-Gly at biological pH.

Question 76

Provide the structure of the tripeptide glu-ser-ala at pH 2.

Question 77

In peptide synthesis,give the use of dicyclohexylcarbodiimide.

A)activates the carboxyl group of an amino acid
B)protects the carboxyl group of an amino acid
C)protects the amino group of an amino acid
D)activates the amino group of an amino acid
E)removes the protecting group on the N-terminal amino acid

Question 78

When a disulfide linkage is formed,the compound containing this new linkage has been

A)hydrolyzed.
B)dehydrated.
C)electrolyzed.
D)oxidized.
E)reduced.

Question 79

Provide the structure of the tripeptide val-gly-ser at biological pH.

Question 80

Explain the chemistry behind giving a "permanent" to a head of hair.