Deck 25: Amino Acids, Peptides, and Proteins

Question 1

Which of the following is the zwitterion form of L-alanine?

A)

B)

C)

D)

Answer 1

Question 2

What is the pI of valine, shown below? (the $\mathrm{p} K_{\mathrm{a}}$ 's are shown)

A) 2.32
B) 4.81
C) 5.97
D) 9.62

Answer 2

5.97

Question 3

Which of the following is the major product of the reaction shown below? (the $\mathrm{p} K_{\mathrm{a}}{ }^{\text {'s }}$ are shown)

A)

B)

C)

D)

Answer 3

Question 4

The Fischer projection shown below denotes a amino acid which has the configuration.

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

Question 5

What is the total number of different tripeptides which can result from three different L-amino acids?

A) three
B) four
C) six
D) nine

Question 6

What is the net charge on L-aspartic acid $\left(\mathrm{R}=-\mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\right)$ at a pH of 11.0 ?

A) +1
B) +2
C) -1
D) -2

Question 7

In strongly acidic solution L-lysine is primarily a dication as shown below. As the $\mathrm{pH}$ is raised, which proton is lost to form the monocation?

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

Question 8

Linus Pauling is credited with describing the $\alpha$ -helix structure of a polypeptide. The $\alpha$ -helix is an example of a polypeptide's

A) primary structure.
B) secondary structure.
C) tertiary structure.
D) quaternary structure.

Question 9

What is the net charge on the dipeptide lys-asp at a $\mathrm{pH}$ of 1.0 ?
Aspartic acid $\left(\mathrm{R}=-\mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{H}\right)$
Lysine ( $\left.\mathrm{R}=\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{NH}_{2}\right)$

A) +1
B) +2
C) +3
D) +4

Question 10

A pentapeptide was found to contain the amino acids ala, gly, met, phe, and ser. Partial hydrolysis of the pentapeptide gave the dipeptides gly-ser, met-phe, ala-gly, and ser-met. What is the sequence of the pentapeptide?

A) gly-ser-met-phe-ala
B) gly-ser-met-ala-phe
C) ala-gly-ser-phe-met
D) ala-gly-ser-met-phe

Question 11

Which of the following is the DNP derivative obtained from the reaction sequence shown below?

A)

B)

C)

D)

Question 12

Which one of the following reagents is used for the visual detection of amino acids?

A) Sanger's reagent
B) dicyclohexylcarbodiimide (DCCI)
C) ninhydrin
D) phenyl isothiocyanate

Question 13

Which one of the following is the final product of the reaction sequence shown below?

A)

B)

C)

D)

Question 14

Identify the missing starting reagent needed in the Strecker synthesis of isoleucine. (Assume you will get all the stereoisomers of isoleucine.)

A)

B)

C)

D)

Question 15

In aqueous solution, the artificial sweetener aspartame slowly converts to the cyclic compound shown below. Which of the following best describes this reaction?

A) nucleophilic acyl substitution
B) Dieckmann condensation
C) ester hydrolysis
D) $\mathrm{S}_{\mathrm{N}} 2$ reaction

Question 16

Which of the following is the abbreviated formula of the tetrapeptide shown below? (Hint: Remember to start at the $\mathrm{N}$ -terminal end.)

A) lys-ser-asp-ala
B) ser-lys-ala-asp
C) asp-ala-ser-lys
D) asp-ser-ala-lys