Question 1

Which functional group is responsible for the linkage between amino acids in a peptide chain?

Accepted Answer

Amide bond

Question 2

Which amino acid has a side chain containing a thiol group?

Accepted Answer

Cysteine

Question 3

What is the isoelectric point (pI) of alanine, given its $$pK_a$$ values are $$2.35 ($$carboxyl) and $$9.69 ($$amino)?

Accepted Answer

$$pI = \frac{2.35 + 9.69}{2} = 6.02$$

Question 4

Which amino acid would migrate toward the cathode during electrophoresis at pH 7?

Accepted Answer

Arginine

Question 5

Which amino acid is most likely to be found at the origin in paper chromatography due to its high polarity?

Accepted Answer

Glutamate

Question 6

What is the product of mild oxidation of two cysteine molecules?

Accepted Answer

Cystine (disulfide bond formation)

Question 7

Which amino acid has a side chain with a benzene ring?

Accepted Answer

Phenylalanine

Question 8

Which reagent specifically cleaves peptide bonds on the C-side of methionine residues?

Accepted Answer

Cyanogen bromide

Question 9

What is the effect of denaturation on a protein’s structure?

Accepted Answer

Destroys the tertiary structure

Question 10

Which amino acid is an imidazole-substituted alanine?

Accepted Answer

Histidine

Question 11

Which amino acid is essential and contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 12

What is the charge of the carboxyl group of an amino acid at pH 7?

Accepted Answer

Negative

Question 13

Which amino acid would be cleaved by elastase, but not if proline is at the cleavage site?

Accepted Answer

Glycine

Question 14

Which of the following is a peptide hormone that regulates water retention in the body?

Accepted Answer

Vasopressin

Question 15

What is the correct sequence of steps for determining the amino acid sequence of a protein?

Accepted Answer

Break disulfide bridges, hydrolyze peptide bonds, identify N-terminal and C-terminal amino acids

Question 16

Which amino acid is most likely to be found in the interior of a protein due to its hydrophobic side chain?

Accepted Answer

Leucine

Question 17

What is the effect of removing the t-Boc protecting group during peptide synthesis?

Accepted Answer

Exposes the amino group for further peptide bond formation

Question 18

Which amino acid has the lowest isoelectric point (pI) among the following: alanine, lysine, glutamic acid?

Accepted Answer

Glutamic acid

Question 19

Which enzyme cleaves peptide bonds on the C-side of aromatic amino acids such as phenylalanine, tyrosine, and tryptophan?

Accepted Answer

Chymotrypsin

Question 20

What is the overall yield of an octapeptide if each peptide bond formation has an 80% yield?

Accepted Answer

$$0.8^7 = 0.21$ (21%)

Amino Acids, Peptides, and Proteins: Structure, Properties, and Synthesis

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