Deck 27: Amino Acids and Proteins

Question 1

Why is the s-trans form of an amide bond more stable?

A)There is no s-cis form in an amide bond.
B)The oxygen is hydrogen-bonded with the nitrogen atom.
C)The nitrogen is able to be sp²-hybridized.
D)The more sterically bulky groups are farther apart.

Answer 1

The more sterically bulky groups are farther apart.

Question 2

What are the basic steps in the Merrifield peptide synthesis?

A)Coupling and hydrolysis
B)Hydrolysis and deprotection
C)Deprotection and hydrogenation
D)Coupling and deprotection

Answer 2

Coupling and deprotection

Question 3

What amino acid is at the C-terminus of the following peptide?

A)Valine
B)Serine
C)Alanine
D)Proline

Answer 3

Alanine

Question 4

What reagents would you use to convert acetaldehyde into alanine?

A)NH₃
B)HCN
C)NaCN,NH₄Cl
D)NaNH₂

Question 5

Which of the following aldehydes would be a good starting material in the Strecker synthesis of phenylalanine?

A)A
B)B
C)C
D)D

Question 6

Which of the following compounds is not an amino acid?

A)A
B)B
C)C
D)D

Question 7

Which of the following is the correct structure for aspartic acid at pH = 1?

A)A
B)B
C)C
D)D

Question 8

Which is the correct structure for the amino acid cysteine?

A)A
B)B
C)C
D)D

Question 9

Why do amide bonds exist as reasonably stable s-cis or s-trans isomers at room temperature?

A)These amide bonds are not stable.
B)There is partial double bond character between the carbonyl carbon and the nitrogen atom.
C)The oxygen atom is hydrogen-bonded with the nitrogen atom.
D)The side-chains can form hydrogen bonds.

Question 10

Which is the correct structure for serine?

A)A
B)B
C)C
D)D

Question 11

Which of the following is the major advantage of the Merrifield synthesis of peptides?

A)It allows for the formation of absolutely no by-products.
B)Impurities can be easily washed away.
C)Excess reagent can be used.
D)It prevents hydrogenation.

Question 12

Which of the following is the structure of the amino acid lysine?

A)A
B)B
C)C
D)D

Question 13

Which of the following is the correct structure for alanine at pH = 7?

A)A
B)B
C)C
D)D

Question 14

Which is the correct structure for the amino acid proline?

A)A
B)B
C)C
D)D

Question 15

Which is the correct structure for the amino acid valine?

A)A
B)B
C)C
D)D

Question 16

What is the separation of a racemic mixture into its component enantiomers called?

A)Diastereomers
B)Meso
C)Resolution
D)Neutralization

Question 17

What amino acid is at the N-terminus of the following peptide?

A)Valine
B)Serine
C)Alanine
D)Proline

Question 18

Why does the formation of salts of a racemic mixture of N-acetyl valine with a single enantiomer of a-methylbenzylamine enable the separation of the two enantiomers of N-acetyl valine?

A)They form amides.
B)They form diastereomers.
C)They form salts.
D)They form meso compounds.

Question 19

Why can glycine not be resolved into two enantiomers?

A)It has no stereogenic centers.
B)It has no nitrogen atoms.
C)It has no aromatic rings.
D)It cannot be converted into a salt.

Question 20

What is the configuration of naturally occurring amino acids?

A)D
B)S
C)L
D)R

Question 21

What are the only covalent bonds that stabilize the tertiary structure of a peptide?

A)Hydrogen bonds
B)Disulfide bonds
C)Van der Waal bonds
D)Ionic bonds

Question 22

What is the IUPAC or common name for the following compound?

A)Cysteinylalanine
B)Alanylcysteine
C)Serinylalanine
D)Alanylserine

Question 23

What is the major organic product for the following reaction?

A)A
B)B
C)C
D)D

Question 24

Give the order (1^st to last)in which the following amino acids would be eluted with a buffer of pH = 4 from a column containing a cationic-exchange resin (Dowex 50): Arg (pI = 10.8),Ser (pI = 5.7),Asp (pI = 2.8)and His (pI = 7.6).

A)His,Ser,Asp,Arg
B)Arg,His,Ser,Asp
C)His,Ser,Arg,Asp
D)Asp,Ser,His,Arg

Question 25

Which of the following amino acids does not have an L-isomer?

A)Alanine
B)Valine
C)Glycine
D)Leucine

Question 26

Which of the following correctly describes the tertiary structure of a peptide?

A)the three-dimensional conformations of localized regions of a protein
B)the particular sequence of amino acids that are joined together by peptide bonds
C)the structure is defined by the b-pleated sheet form
D)the three-dimensional shape adopted by the entire peptide

Question 27

Which of the following is (are)globular protein(s)?

A)Hemoglobin
B)Keratins
C)Collagens
D)Elastins

Question 28

What is the appropriate sequence of reaction conditions used to synthesize valine from acetamidomalonic ester?

A)(1)NaOH; (2)(CH₃)₂CHBr; (3)Cl₂,H₂O,heat
B)(1)NaOCH₂CH₃; (2)(CH₃)₂CH₂CHBr; (3)HCl,H₂O,heat
C)(1)NaOCH₂CH₃; (2)(CH₃)₂CHBr; (3)HCl,H₂O,heat
D)(1)NaOH; (2)CH₃CH₂CH₂Br; (3)HCl,H₂O,heat

Question 29

Which of the following amino acids is achiral?

A)Phenylalanine
B)Glycine
C)Valine
D)Alanine

Question 30

Which of the following correctly describes a protein?

A)a dipeptide; two amino acids joined together by one amide bond
B)a tripeptide; three amino acids joined together by two amide bonds
C)a polymer of more than 40 amino acids joined together by amide bonds
D)a polypeptide of any number of amino acids joined together by amide bonds

Question 31

Which one of the following naturally occurring amino acids does not have an S configuration?

A)Cysteine
B)Alanine
C)Tyrosine
D)Isoleucine

Question 32

What is formed by the combination of four amino acids?

A)A protein
B)A polypeptide
C)A tripeptide
D)A tetrapeptide

Question 33

Reaction of a polypeptide,composed of 12 amino acids,with carboxypeptidase A releases Met (C-terminal amino acid).The polypeptide undergoes partial hydrolysis to give 12 groups of peptides.Use the groups of overlapping amino acids to determine the proper sequence of this polypeptide.Note: Since these lists of peptides are separated by commas,they are not necessarily in the proper sequence. Ser,Lys,Trp-5.Met,Ala,Gly- 9.Lys,Ser
Gly,His,Ala-6.Ser,Lys,Val -10.Glu,His,Val
Glu,Val,Ser-7.Glu,His-11.Trp,Leu,Glu
Leu,Glu,Ser-8.Leu,Lys,Trp-12.Ala,Met

A)Met-Ala-Gly-His-Glu-Val-Ser-Lys-Trp-Leu-Glu-Ser
B)Met-Ala-Gly-Glu-His-Ser-Val-Lys-Trp-Leu-Glu-Ser
C)Ser-Glu-Leu-Trp-Lys-Ser-Val-Glu-His-Gly-Ala-Met
D)Ser-Lys-Leu-Trp-Lys-Ser-Val-His-Glu-Gly-Ala-Met

Question 34

What is (are)the missing reagent(s)in the reaction below?

A)NH₃
B)HCN
C)NaCN,NH₄Cl
D)NaNH₂

Question 35

Below is a 2D chromatogram that shows the separation of five amino acids.In this technique,the amino acid mixture is first separated by chromatography using a polar solvent system.Then the plate is rotated 90°,and the amino acids are further separated by electrophoresis.Identify the spots obtained from a mixture of Trp,Glu,Lys,Ile and Thr.A table with isoelectric points is included to aid in solving this problem. amino acid-pI value Trp-5.9
Glu-3.2
Lys-9.7
Ile-6.0
Thr-5.6

A)1=Lys,2=Thr,3=Glu,4=Trp,5=Ile
B)1=Glu,2=Thr,3=Lys,4=Trp,5=Ile
C)1=Lys,2=Ile,3=Glu,4=Trp,5=Thr
D)1=Glu,2=Ile,3=Lys,4=Trp,5=Thr

Question 36

Amino acid synthesis is possible by all except one of the pathways listed.Which is not a synthetic pathway for amino acids?

A)Amination of malonic ester followed by hydrolysis and decarboxylation
B)Nucleophilic addition of NH₃ to an aldehyde followed by addition of cyanide to the imine,and,finally,hydrolysis
C)S_N2 reaction using an a-halo carboxylic acid with ammonia as the nucleophile
D)Reaction of NH₄Cl and NaCN with an aldehyde followed by an acidic work-up

Question 37

Below is a proposed method for resolving a racemic mixture of (R)- and (S)-phenylalanine.Upon separation of the products,will this method produce (R)- or (S)-phenylalanine?

A)(R)-Phenylalanine is produced since the acylase only hydrolyzes the amides of L-amino acids.
B)(S)-Phenylalanine is produced since the acylase only hydrolyzes the amides of L-amino acids.
C)(R)-Phenylalanine is produced since the acylase only hydrolyzes the amides of D-amino acids.
D)(S)-Phenylalanine is produced since the acylase only hydrolyzes the amides of D-amino acids.

Question 38

Which of the following is (are)fibrous protein(s)?

A)Keratins
B)Hormones
C)Enzymes
D)Antibodies

Question 39

Which of the following correctly describes a peptide bond?

A)a bond between sp³-hybridized atoms only
B)a bond usually found in the s-cis conformation
C)an amide bond
D)the result of the formation of the carbonyl group of one amino acid with a R-group from the other amino acid

Question 40

Which of the following correctly describes the Merrifield synthesis?

A)It uses a solid phase technique for the synthesis of peptides.
B)It uses DCC (dicyclohexylcarbodiimide)to form the amide bond in a peptide synthesis.
C)It uses BOC (tert-butoxycarbonyl)as a protecting group for peptide synthesis.
D)It uses aqueous phase techniques for the synthesis of large polypeptides.

Question 41

What is the product of the following reaction? (Assume workup to neutralize.)

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

Question 42

What is the product of the following reaction? (Assume workup to neutralize.)

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

Question 43

What is the product of the following reaction? (Assume workup to neutralize.)

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

Question 44

What is the major organic product for the following reaction?

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

Question 45

What is the product of the following reaction? (Assume workup to neutralize.)

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

Question 46

What is the name given to the pH at which the concentration of the zwitterionic form of an amino acid is at a maximum concentration?

A)Electric point
B)Dipolar point
C)Neutral point
D)Isoelectric point