Deck 15: Biomolecules: Amino Acids, Peptides, and Proteins

Question 1

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. Draw the structure of the predominant form of leucine at pH = 1.50.

Answer 1

Question 2

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. How many possible stereoisomers of leucine are there?

Answer 2

Since leucine has one chirality center, there are 2¹, or 2 possible leucine stereoisomers.

Question 3

Instructions: Match a structure from the list below to each of the following terms.

Answer 3

Question 4

Instructions: Consider the following structure. Based on this structure answer the following question(s). Refer to instructions. How many other peptides could be formed from this same combination of amino acids?

A) 3
B) 6
C) 9
D) 12

Question 5

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. Draw the condensed structure for leucine, and label all chirality centers with an asterisk and identify the amine as primary, secondary or tertiary.

Question 6

Instructions: Consider the following structure. Based on this structure answer the following question(s). Refer to instructions. Circle the peptide bonds.

Question 7

Instructions: Refer to the data below to answer the following question.
Refer to inatructions. The most acidic amino acid is ____.

Question 8

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. What is the pI of leucine?

Question 9

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. Draw a Fischer projection of L-leucine and label the chirality center(s) as R or S.

Question 10

Instructions: Consider the following structure. Based on this structure answer the following question(s). Refer to instructions. Name the peptide using both the three-letter and one-letter codes.

Question 11

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. Leucine is described as an essential amino acid. What does this mean?

Question 12

Which of the following amino acids would contain the highest concentration of zwitterions at pH 5.90?

A) aspartic acid (pI 2.77)
B) alanine (pI 6.01)
C) lysine (pI 9.74)
D) glutamic acid (pI 3.22)
E) all of these contain approximately equal concentrations of zwitterions

Question 13

Instructions: Refer to the data below to answer the following question(s).
Porcine dynorphin is a neuropeptide having 17 amino acid residues. Its structure is shown below.
Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-Trp-Asp-Asn-Gln
Refer to instructions. What fragments would result if dynorphin were cleaved by chymotropsin?

Question 14

Instructions: Refer to the data below to answer the following question(s).
Porcine dynorphin is a neuropeptide having 17 amino acid residues. Its structure is shown below.
Tyr-Gly-Gly-Phe-Leu-Arg-Arg-Ile-Arg-Pro-Lys-Leu-Lys-Trp-Asp-Asn-Gln
Refer to instructions. What fragments would result if dynorphin were cleaved by trypsin?

Question 15

Write the equation for the reaction, using methanol (CH₃OH), that would render the carboxyl group of alanine unreactive.

Question 16

Instructions: Refer to the data below to answer the following question.
Refer to instructions. The most basic amino acid is __________.

Question 17

Define isoelectric point.

Question 18

Instructions: Refer to the data below to answer the following question.
Refer to instructions. At what pH would you carry out an electrophoresis experiment if you wanted to separate a mixture of lysine, aspartic acid and phenylalanine? Explain.

Question 19

Instructions: Consider the following structure. Based on this structure answer the following question(s). Refer to instructions. Identify the C-terminal amino acid and the N-terminal amino acid.

Question 20

Instructions: Refer to the data below to answer the following question(s).
Leucine is an essential amino acid with the systematic name 2-amino-3-methylpentanoic acid. It has pK_a1 = 2.36 and pK_a2 = 9.60.
Refer to instructions. Draw the structure of the predominant form of leucine at pH = 10.00.

Question 21

Which of the following reagents can be used to cleave a tert-butoxycarbonyl (Boc) protecting group from a peptide?

A) H₂/Pd
B) CF₃CO₂H
C) Na₂CO₃, H₂O
D) LiAlH₄

Question 22

What are the R/S designations of the two stereocenters of L-threonine?

A) 2R,3R
B) 2R,3S
C) 2S,3R
D) 2S,3S

Question 23

Show the steps involved in a synthesis of F-G-I using the Merrifield procedure.

Question 24

BOC protecting groups are generally removed by treatment with trifluoroacetic acid. On the structures provided below, draw arrows consistent with electron flow in the mechanism of this reaction.

Question 25

To what structural feature does the term "tertiary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 26

Which of the following amino acids is a secondary amine?

A) proline
B) glutamine
C) histidine
D) aspargine

Question 27

Which of the following amino acids has a non-polar side chain?

A) histidine
B) arginine
C) glutamine
D) valine

Question 28

To what structural feature does the term "secondary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 29

Which of the following tripeptides is not hydrolysed by chymotrypsin?

A) Phe-Lys-Glu
B) Lys-Tyr-Phe
C) Gln-Ser-Phe
D) Gln-Tyr-Ser

Question 30

Instructions: Match a term from the list below to each definition.

Question 31

Which of the following tripeptides is not hydrolysed by trypsin?

A) Glu-Arg-Ser
B) Arg-Glu-Thr
C) Glu-Ser-Arg
D) Lys-Ser-Arg

Question 32

Which of the following amino acids migrates to the negative electrode on paper electrophoresis at a pH of 7.0?

A) lysine
B) aspartic acid
C) asparagine
D) glutamic acid

Question 33

Refer to the data below to answer the following questions:
The octapeptide saralasin is a specific antagonist of angiotensin II. A derivative of saralasin is used therapeutically as an antihypertensive. Amino acid analysis of saralasin show the presence of the following amino acids:
Ala, Arg, His, Pro, Sar, Tyr, Val₂
Refer to instructions. Partial hydrolysis of saralasin with dilute hydrochloric acid yields the following fragments:
Tyr-Val-His
Sar-Arg-Val
His-Pro-Ala
Val-Tyr-Val
Arg-Val-Tyr
What is the structure of saralasin?
Sar-Arg-Val
Arg-Val-Tyr
Val-Tyr-Val
Tyr-Val-His
His-Pro-Ala

Question 34

An enzyme classified as a ligase would be associated with a reaction than involves the:

A) introduction of a double bond.
B) loss of water.
C) loss of carbon dioxide.
D) transfer of an amino group.
E) hydrolysis of an ester.

Question 35

To what structural feature does the term "primary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides

Question 36

Which of the following amino acids has an aromatic side chain?

A) isoleucine
B) valine
C) tyrosine
D) threonine

Question 37

Refer to the data below to answer the following questions:
The octapeptide saralasin is a specific antagonist of angiotensin II. A derivative of saralasin is used therapeutically as an antihypertensive. Amino acid analysis of saralasin show the presence of the following amino acids:
Ala, Arg, His, Pro, Sar, Tyr, Val₂
Refer to instructions. Sar is the mnemonic for sarcosine, N-methyl aminoethanoic acid. Draw the structure of sarcosine.

Question 38

Which of the following amino acids migrates to the positive electrode on paper electrophoresis at a pH of 7.0?

A) glutamic acid
B) arginine
C) lysine
D) histadine

Question 39

Which of the following amino acids has a sulfur-containing side chain?

A) serine
B) cysteine
C) lysine
D) methionine
E) both b and d

Question 40

To what structural feature does the term "quaternary structure" refer?

A) the sequence of amino acids in proteins
B) the overall folding pattern of proteins
C) the aggregation of polypeptides
D) the conformation of local regions of polypeptides