Question 1

Which of the following amino acids contains a sulfur atom in its side chain and is classified as nonpolar?

Accepted Answer

Methionine (Met)

Question 2

A patient is diagnosed with a genetic disorder that affects the breakdown of phenylalanine. Which property of phenylalanine makes it essential to monitor in the patient's diet?

Accepted Answer

It is nonpolar and aromatic, making it hydrophobic and likely to accumulate in tissues.

Question 3

Which amino acid is most likely to form disulfide bonds, stabilizing the tertiary structure of proteins?

Accepted Answer

Cysteine (Cys)

Question 4

Given the following R group: $\mathrm{CH_2COO^-}$, which amino acid does it represent and what is its property at physiological pH?

Accepted Answer

Aspartic acid (Asp); acidic and negatively charged

Question 5

Which of the following amino acids is classified as basic and contains a guanidinium group in its side chain?

Accepted Answer

Arginine (Arg)

Question 6

A mutation replaces a glutamic acid residue with valine in a hemoglobin molecule. Which of the following best describes the chemical consequence of this substitution?

Accepted Answer

A negatively charged, hydrophilic side chain is replaced by a nonpolar, hydrophobic side chain.

Question 7

Which amino acid is most likely to be found at the active site of an enzyme that catalyzes acid-base reactions near physiological pH due to its side chain pKa?

Accepted Answer

Histidine (His)

Question 8

Which of the following amino acids has a side chain that can form hydrogen bonds but is not charged at physiological pH?

Accepted Answer

Serine (Ser)

Question 9

A protein is found to be embedded within the hydrophobic core of a cell membrane. Which amino acid is most likely to be abundant in the transmembrane region?

Accepted Answer

Leucine (Leu)

Question 10

Which of the following best describes the difference between asparagine (Asn) and aspartic acid (Asp)?

Accepted Answer

Asparagine has an amide group in its side chain, while aspartic acid has a carboxyl group.

Question 11

Which amino acid is most likely to disrupt an alpha helix due to its rigid ring structure?

Accepted Answer

Proline (Pro)

Question 12

A researcher is studying a protein that binds DNA. Which amino acid is most likely to be involved in binding the negatively charged phosphate backbone of DNA?

Accepted Answer

Lysine (Lys)

Question 13

Which of the following amino acids is aromatic and can participate in stacking interactions with nucleic acid bases?

Accepted Answer

Tryptophan (Trp)

Question 14

Which amino acid is most likely to be phosphorylated during cell signaling events?

Accepted Answer

Threonine (Thr)

Question 15

A peptide has the following sequence: Ala-Glu-Lys-Ser. At physiological pH ($pH = 7.4$), what is the net charge of this peptide?

Accepted Answer

$+1$

Question 16

Which amino acid has a side chain that can act as both a hydrogen bond donor and acceptor, and is classified as polar but uncharged?

Accepted Answer

Glutamine (Gln)

Question 17

Which of the following amino acids is most likely to be found on the surface of a soluble, globular protein in the cytoplasm?

Accepted Answer

Threonine (Thr)

Question 18

A mutation changes a codon for arginine to a codon for glycine. Which of the following best describes the change in side chain properties?

Accepted Answer

From a basic, positively charged side chain to a nonpolar, small side chain

Question 19

Which amino acid is most likely to be involved in N-linked glycosylation of proteins?

Accepted Answer

Asparagine (Asn)

Question 20

Which of the following best explains why tyrosine is classified as both aromatic and polar?

Accepted Answer

It contains a phenol group, which is aromatic and can form hydrogen bonds.

UNIT 1: Amino Acids and Their Properties: Structure, Classification, and Identification

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