Question 1

Which of the following statements best describes the main stabilizing force in the formation of an α-helix in proteins?

Accepted Answer

Hydrogen bonds between the carbonyl oxygen of one peptide bond and the amide hydrogen of another peptide bond four residues away

Question 2

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

Accepted Answer

The triple helix will be destabilized because the bulky side chain cannot fit in the center.

Question 3

Which of the following best explains why proline is often found at the turns of polypeptide chains and disrupts α-helices?

Accepted Answer

Proline's ring structure restricts rotation and introduces a kink in the polypeptide backbone.

Question 4

Which of the following is a correct statement about the quaternary structure of hemoglobin?

Accepted Answer

It is composed of four subunits, each containing a heme group.

Question 5

A patient presents with symptoms of scurvy, including bleeding gums and poor wound healing. Which biochemical process is most directly impaired?

Accepted Answer

Hydroxylation of proline and lysine residues in collagen

Question 6

Which of the following best describes the hydrophobic effect in protein folding?

Accepted Answer

Hydrophobic side chains cluster in the protein interior, releasing ordered water molecules and increasing solvent entropy.

Question 7

Which equation correctly represents the relationship between Gibbs free energy, enthalpy, and entropy in protein folding?

Accepted Answer

$$\Delta G = \Delta H - T \cdot \Delta S$$

Question 8

Which of the following is a characteristic feature of β-sheets in proteins?

Accepted Answer

Side chains project outward from the sheet, alternating above and below the plane.

Question 9

Which of the following best explains why silk fibroin is strong but flexible?

Accepted Answer

It is composed of stacked antiparallel β-sheets with weak van der Waals interactions between side chains.

Question 10

Which of the following is NOT a common factor that can denature proteins?

Accepted Answer

Mild agitation at room temperature

Question 11

A protein is found to have a domain that binds ATP and another domain that binds DNA. What is the best description of this protein's structure?

Accepted Answer

It is a globular protein with multiple domains, each with a distinct function.

Question 12

Which of the following amino acids is most likely to be found in the interior of a globular protein?

Accepted Answer

Leucine

Question 13

Which of the following best describes the role of disulfide bonds in protein structure?

Accepted Answer

They form covalent links between cysteine residues, stabilizing tertiary and quaternary structure.

Question 14

Which of the following is a correct statement about amyloid fibrils?

Accepted Answer

They are highly ordered aggregates rich in β-sheet structure.

Question 15

A protein is denatured by urea and then allowed to refold after urea is removed. Which statement best describes the outcome?

Accepted Answer

The protein may regain its original structure if the amino acid sequence contains all the information for folding.

Question 16

Which of the following best explains why vitamin C deficiency leads to weakened connective tissue?

Accepted Answer

Vitamin C is required for the hydroxylation of proline and lysine in collagen, stabilizing the triple helix.

Question 17

Which of the following is a key difference between parallel and antiparallel β-sheets?

Accepted Answer

Antiparallel β-sheets have hydrogen bonds that are more linear and stronger than those in parallel β-sheets.

Question 18

Which of the following best describes the amphipathic nature of some α-helices and β-sheets?

Accepted Answer

They have hydrophobic side chains on one face and hydrophilic side chains on the opposite face.

Question 19

Which of the following is a common feature of fibrous proteins such as keratin, fibroin, and collagen?

Accepted Answer

They have repetitive amino acid sequences that favor extended secondary structures.

Question 20

Which of the following best explains the molecular basis of prion diseases?

Accepted Answer

They are caused by the accumulation of misfolded proteins with high β-sheet content that induce misfolding in normal proteins.

The Three-Dimensional Structure of Proteins: Secondary, Tertiary, and Quaternary Organization

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