Question 1

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

Accepted Answer

The sequence of amino acids in a polypeptide chain, connected by covalent peptide bonds.

Question 2

Which type of interaction is primarily responsible for driving the folding of a globular protein into its tertiary structure?

Accepted Answer

Hydrophobic interactions that bury nonpolar side chains in the protein interior.

Question 3

A Ramachandran plot is used to visualize which of the following properties of a polypeptide chain?

Accepted Answer

The sterically allowed values of the backbone torsion angles $$\phi$$ and $$\psi.$$

Question 4

Which amino acid is most likely to disrupt an α helix due to its conformational flexibility?

Accepted Answer

Glycine

Question 5

In the context of protein structure, what is the main difference between a motif and a domain?

Accepted Answer

A motif is a small folding topology found in many proteins, while a domain is a larger, independently stable structural unit.

Question 6

Which of the following statements about β sheets is correct?

Accepted Answer

Antiparallel β sheets are more stable than parallel β sheets due to more optimal hydrogen bonding geometry.

Question 7

A protein is denatured by heating above its melting temperature $$T_m. $$What is the most likely molecular explanation for the loss of function?

Accepted Answer

Disruption of weak noncovalent interactions leads to unfolding and loss of the specific three-dimensional structure required for function.

Question 8

Which repeating sequence is characteristic of the primary structure of collagen?

Accepted Answer

A repeating (Gly–Pro–Pro/Hyp)$$_n$$ motif

Question 9

Which of the following best explains why the folding of a protein is entropically favorable for the solvent?

Accepted Answer

Folding buries nonpolar residues, liberating ordered water molecules and increasing the entropy of the solvent.

Question 10

Which of the following is NOT a typical advantage of quaternary structure in proteins?

Accepted Answer

Increased susceptibility to denaturation by chaotropic agents

Question 11

A mutation replaces a glycine residue in the center of a collagen triple helix with alanine. What is the most likely structural consequence?

Accepted Answer

The triple helix will be destabilized because only glycine fits in the crowded center.

Question 12

Which of the following statements about protein folding is supported by Levinthal’s paradox?

Accepted Answer

Proteins must fold via specific pathways rather than by random sampling of all possible conformations.

Question 13

Which of the following best describes the role of molecular chaperones in protein folding?

Accepted Answer

They assist in the proper folding of proteins and prevent aggregation, often using ATP.

Question 14

Which of the following is a key feature of intrinsically disordered proteins?

Accepted Answer

They lack a stable three-dimensional structure until they bind to their target molecules.

Question 15

Which of the following best explains why α helices and β sheets are commonly found in the core of globular proteins?

Accepted Answer

Their extensive hydrogen bonding neutralizes backbone amides, making them compatible with the hydrophobic core.

Question 16

A protein is found to have a quaternary structure with open symmetry. Which of the following is the best example of such a protein?

Accepted Answer

A microtubule composed of α- and β-tubulin dimers.

Question 17

Which of the following best describes the energetic stability of most folded globular proteins?

Accepted Answer

They are only marginally stable, with $$\Delta G$$ values of $$-5 to$$ $$-10 kJ $$mol$$^{-1}.$$

Question 18

Which of the following is a correct statement about the handedness of the α helix in proteins composed of L-amino acids?

Accepted Answer

The α helix is right-handed, with 3.6 residues per turn.

Question 19

Which of the following best explains why proline is often found in β turns but rarely in α helices?

Accepted Answer

Proline's rigid ring structure restricts its φ angle, making it suitable for tight turns but disruptive to the α helix.

Proteins: Three-Dimensional Structure – Study Notes

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