Deck 22: Amino Acids and Proteins

Question 1

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

Answer 1

(S)-Phenylalanine is produced since the acylase only hydrolyzes the amides of L-amino acids.

Question 2

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

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

Answer 2

(1) NaOCH₂CH₃; (2) (CH₃)₂CHBr; (3) HCl, H₂O, heat

Question 3

Which of the following correctly describes the Merrifield synthesis?

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

Answer 3

It uses BOC (tert-butoxycarbonyl) as a protecting group for peptide synthesis.

Question 4

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

Question 5

Iosmerase performs the following function:

A) Catalyzes the hydrolysis of esters, amides, and other functional groups that are cleaved when they react with water
B) Catalyzes the conversion of one isomer to another
C) Catalyzes oxidation-reduction reactions
D) Catalyzes the transfer of a group from one molecule to another

Question 6

Amino acid synthesis is possible by allexcept one of the pathways listed. Which isnot a synthetic pathway for amino acids?

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

Question 7

Transferase performs the following function:

A) Catalyzes the transfer of a group from one molecule to another
B) Catalyzes oxidation-reduction reactions
C) Catalyzes the conversion of one isomer to another
D) Catalyzes the hydrolysis of esters, amides, and other functional groups that are cleaved when they react with water

Question 8

Oxidoreductase performs the following function:

A) Catalyzes the hydrolysis of esters, amides, and other functional groups that are cleaved when they react with water
B) Catalyzes the transfer of a group from one molecule to another
C) Catalyzes the conversion of one isomer to another
D) Catalyzes oxidation-reduction reactions

Question 9

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

Question 10

Hydrolase performs the following function:

A) Catalyzes the hydrolysis of esters, amides, and other functional groups that are cleaved when they react with water
B) Catalyzes the transfer of a group from one molecule to another
C) Catalyzes the conversion of one isomer to another
D) Catalyzes oxidation-reduction reactions

Question 11

Which of the following compounds is not an amino acid?

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