Question 1

Which of the following conclusions was supported by Anfinsen’s classic ribonuclease A renaturation experiments?

Accepted Answer

A protein’s primary sequence contains all the information necessary for folding into its native structure.

Question 2

What is the primary driving force for protein folding under physiological conditions?

Accepted Answer

Hydrophobic effect, which increases entropy of water molecules

Question 3

A protein is denatured in 8M urea and mercaptoethanol. After removal of both reagents, the protein regains its native structure and activity. What does this experiment demonstrate?

Accepted Answer

The native structure is the thermodynamically favored state.

Question 4

Which statement best describes the role of hydrogen bonds in protein folding?

Accepted Answer

Hydrogen bonds define protein structure but are not the primary source of stability.

Question 5

Why are unpaired charges in the interior of a protein generally unfavorable?

Accepted Answer

They result in a high desolvation cost due to removal from water.

Question 6

Which of the following best describes the folding funnel model of protein folding?

Accepted Answer

Proteins fold via multiple pathways, reducing free energy and entropy toward the native state.

Question 7

A protein is heated above its melting temperature ($$T_m). $$What is most likely to occur?

Accepted Answer

The protein will denature, losing its secondary and tertiary structure.

Question 8

Which of the following diseases is associated with protein misfolding and aggregation into amyloid fibrils?

Accepted Answer

Alzheimer’s disease

Question 9

What is the main function of molecular chaperones such as GroEL/GroES?

Accepted Answer

To prevent aggregation and assist in proper protein folding

Question 10

Which structural feature is characteristic of keratin, a fibrous protein found in hair and nails?

Accepted Answer

Coiled-coil of α-helices stabilized by hydrophobic interactions and disulfide bonds

Question 11

Why does silk fibroin not stretch easily?

Accepted Answer

Its β-sheet structure is already fully extended.

Question 12

Which amino acid sequence is most commonly found in collagen?

Accepted Answer

Gly-Pro-HyP

Question 13

What is the biochemical cause of scurvy?

Accepted Answer

Impaired hydroxylation of proline in collagen due to lack of vitamin C

Question 14

Which of the following best explains why hydrogen bonds are not the main driving force for protein folding?

Accepted Answer

Hydrogen bonds with water in the unfolded state must be broken, incurring a desolvation cost.

Question 15

Which of the following statements about protein-ligand interactions is correct?

Accepted Answer

Protein-ligand interactions are typically reversible, transient, and specific.

Question 16

Which hypothesis suggests that the binding site of a protein is a perfect match for its ligand?

Accepted Answer

Lock and key hypothesis

Question 17

Which of the following is a consequence of the cooperative nature of protein folding, as seen in thermal denaturation curves?

Accepted Answer

Protein unfolding is abrupt, with most structure lost in a narrow temperature range.

Question 18

Which of the following best describes the role of salt bridges in protein structure?

Accepted Answer

Interior salt bridges contribute specificity, but exterior salt bridges contribute little due to water competition.

Question 19

A mutation replaces a glycine in the collagen sequence with a bulky amino acid. What is the most likely effect?

Accepted Answer

The triple helix will be destabilized due to steric hindrance.

Question 20

Which of the following best explains why hair splits easily along the fiber axis but fingernails tend to split across the nail?

Accepted Answer

Keratin fibrils are oriented parallel to the fiber axis in hair and perpendicular in fingernails.

Protein Folding, Stability, and Fibrous Proteins: Structure and Function

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