Question 1

Which of the following statements best describes the structure of an α-amino acid at neutral pH?

Accepted Answer

The amino group is protonated and the carboxylic acid group is deprotonated, forming a zwitterion.

Question 2

Which amino acid does NOT contain a chiral (asymmetric) α-carbon?

Accepted Answer

Glycine

Question 3

L-alanine and D-alanine are examples of which type of stereoisomers?

Accepted Answer

Enantiomers

Question 4

Which of the following amino acids would absorb the most UV light at 280 nm?

Accepted Answer

Tryptophan

Question 5

What is the typical pKa range for the α-amino group of an amino acid?

Accepted Answer

$$8.0 - 9.0$$

Question 6

A peptide bond forms between which two functional groups of adjacent amino acids?

Accepted Answer

The amino group of one amino acid and the carboxyl group of another

Question 7

Which statement best explains why peptide bond formation is not thermodynamically favorable under physiological conditions?

Accepted Answer

It is a condensation reaction that must be coupled to ATP hydrolysis.

Question 8

Which property of the peptide bond contributes most to its planarity and stability?

Accepted Answer

Delocalization of electrons creating partial double-bond character

Question 9

Which of the following best describes the effect of increasing pH on the overall charge of a peptide?

Accepted Answer

The overall charge becomes more negative.

Question 10

Which of the following is a common posttranslational modification of amino acids that can play a role in signaling pathways?

Accepted Answer

Phosphorylation of serine

Question 11

Which enzyme would cleave a peptide bond on the C-terminal side of lysine (K) or arginine (R), except when followed by proline?

Accepted Answer

Trypsin

Question 12

A peptide is boiled in 6N HCl for 24 hours. What is the most likely outcome?

Accepted Answer

The peptide is hydrolyzed into free amino acids.

Question 13

Which of the following modifications would block the N-terminus of a peptide?

Accepted Answer

N-formyl group

Question 14

If a tetrapeptide contains the following ionizable groups: α-carboxyl (pKa = 2.0), side chain carboxyl (pKa = 4.2), α-amino (pKa = 9.0), and side chain amino (pKa = 10.0), what is the net charge at pH 1.0?

Accepted Answer

+2

Question 15

Which of the following best describes an oligopeptide?

Accepted Answer

A peptide chain with 3–15 residues

Question 16

Which of the following statements about proteases is TRUE?

Accepted Answer

Proteases are enzymes that cleave specific peptide bonds.

Question 17

Which of the following is a real-life application of peptide bond cleavage specificity?

Accepted Answer

Predicting the fragments produced by trypsin digestion of a protein during mass spectrometry analysis

Question 18

Which of the following best explains why posttranslational modifications are important for protein function?

Accepted Answer

They change the behavior of proteins, allowing for regulation such as gene expression or suppression.

Question 19

Which of the following statements about the titration curve of histidine is correct?

Accepted Answer

The pI is the pH at which the net charge on the molecule is zero.

Question 20

Which of the following best describes the effect of posttranslational phosphorylation of serine in a protein?

Accepted Answer

It introduces a negative charge, which can alter protein activity or signaling.

Amino Acids and Peptides: Structure, Properties, and Reactions

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