Question 1

Which of the following amino acids is classified as aromatic and is also hydrophobic according to the Kyte & Doolittle hydrophobicity scale?

Accepted Answer

Phenylalanine

Question 2

Which intermolecular force is primarily responsible for stabilizing the α-helix structure in proteins?

Accepted Answer

Hydrogen bonds

Question 3

A mutation replaces a lysine (Lys) residue in a protein with asparagine (Asn), glutamate (Glu), or arginine (Arg). Which substitution is likely to have the least effect on the protein's enzymatic activity and why?

Accepted Answer

Arginine, because it is also basic and positively charged

Question 4

Which amino acid is most likely to be found in abundance in histones and why?

Accepted Answer

Lysine, because it is basic and forms electrostatic interactions with DNA

Question 5

Which of the following best describes the hydrogen bonding pattern in an α-helix?

Accepted Answer

Hydrogen bonds form between the carbonyl oxygen of residue $$n$$ and the amide hydrogen of residue $$n+4$$

Question 6

Which of the following amino acids is technically not hydrophobic, despite being nonpolar?

Accepted Answer

Glycine

Question 7

What is the main reason that arginine (Arg) is more likely to be buried in the interior of proteins compared to lysine (Lys)?

Accepted Answer

Arginine can form more extensive hydrogen bonding networks

Question 8

Which of the following intermolecular forces is most likely to be disrupted when a protein is exposed to extreme pH conditions?

Accepted Answer

Electrostatic interactions

Question 9

Which of the following statements about secondary protein structure is NOT true?

Accepted Answer

The sequence of amino acids has no effect on secondary structure

Question 10

In a β-sheet, what is the orientation of the hydrogen bonds relative to the polypeptide chains?

Accepted Answer

Perpendicular to the direction of the chains

Question 11

Which of the following amino acids contains a sulfur atom in its side chain?

Accepted Answer

Methionine

Question 12

A peptide forms an amphipathic α-helix with nonpolar residues on one side and polar/charged residues on the other. What property does this confer to the peptide?

Accepted Answer

It can interact with both hydrophobic and hydrophilic environments

Question 13

Which of the following best describes the difference between a protein motif and a protein domain?

Accepted Answer

A motif is a recurring structural element, while a domain is a larger, independently folding unit

Question 14

Which of the following amino acids is sometimes charged at physiological pH?

Accepted Answer

Histidine

Question 15

Which of the following is a real-life application of the amphipathic nature of α-helices in proteins?

Accepted Answer

Formation of transmembrane segments in membrane proteins

Question 16

Which of the following equations correctly represents the rise per turn of an α-helix?

Accepted Answer

$$5.4\ 	ext{Å}$$ per turn

Question 17

Which of the following amino acids is classified as both small and polar?

Accepted Answer

Serine

Question 18

Which of the following best explains why Pandinin 2, an amphipathic peptide, can lyse both bacterial and red blood cell membranes?

Accepted Answer

Its amphipathic helix allows it to insert into and disrupt lipid bilayers

Question 19

Which of the following is a correct statement about the orientation of R-groups in an α-helix?

Accepted Answer

They point outward from the center of the helix

Amino Acids and Protein Structure: Properties, Organization, and Stabilizing Forces

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