Question 1

Which of the following statements best describes the general structure of all 20 common amino acids found in proteins?

Accepted Answer

They all have a central carbon atom bonded to a carboxyl group, an amino group, a hydrogen atom, and a unique R group.

Question 2

Which amino acid is the only one that does NOT have a chiral α-carbon?

Accepted Answer

Glycine

Question 3

A patient with phenylketonuria (PKU) cannot metabolize which amino acid to tyrosine?

Accepted Answer

Phenylalanine

Question 4

Which of the following amino acids contains a sulfur atom in its side chain and can form disulfide bonds?

Accepted Answer

Cysteine

Question 5

Which property allows tryptophan and tyrosine to be detected by UV absorption in protein quantification assays?

Accepted Answer

Their aromatic side chains absorb UV light strongly.

Question 6

Which of the following best describes a zwitterion?

Accepted Answer

A molecule with both a positive and a negative charge, but overall neutral.

Question 7

Given the following peptide: Ala-Glu-Gly-Lys, which group will be ionized at neutral pH?

Accepted Answer

The N-terminal α-amino group and the C-terminal α-carboxyl group

Question 8

Which of the following amino acids is classified as a basic (positively charged) amino acid at physiological pH?

Accepted Answer

Arginine

Question 9

A protein is purified using ion-exchange chromatography. Which property of the protein is primarily being exploited?

Accepted Answer

Net charge of the protein

Question 10

Which of the following equations correctly relates the pKa of an amino acid side chain to its acid dissociation equilibrium?

Accepted Answer

$$pK_a = -\log_{10} K_a$$

Question 11

Which of the following best describes the primary structure of a protein?

Accepted Answer

The linear sequence of amino acids linked by covalent bonds

Question 12

Which amino acid is most likely to be found on the interior of a globular protein?

Accepted Answer

Leucine

Question 13

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

Accepted Answer

The α-carboxyl group of one and the α-amino group of the next

Question 14

Which of the following methods is most appropriate for separating proteins based on their size?

Accepted Answer

Gel filtration chromatography

Question 15

Which amino acid can be phosphorylated on its hydroxyl group and is also the smallest polar amino acid?

Accepted Answer

Serine

Question 16

Which of the following best explains why proteins from different species with similar functions often have similar amino acid sequences?

Accepted Answer

Evolutionary conservation of functionally important residues

Question 17

Which of the following amino acids has a side chain that can act as a Brønsted acid or base near physiological pH due to its imidazole group?

Accepted Answer

Histidine

Question 18

A protein sample is analyzed by SDS-PAGE electrophoresis. What property of the proteins primarily determines their migration through the gel?

Accepted Answer

Molecular mass

Question 19

Which of the following best describes the function of mass spectrometry in protein biochemistry?

Accepted Answer

It provides information on molecular mass, amino acid sequence, and the entire proteome.

Question 20

Which of the following is a conjugated protein?

Accepted Answer

Lipoprotein

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

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