Question 1

Which of the following best describes the thermodynamic driving force for protein folding under physiological conditions?

Accepted Answer

A negative change in free energy ($$\Delta G \u003c 0) $$resulting from a balance of enthalpy and entropy contributions.

Question 2

Which of the following interactions is NOT a major contributor to the stabilization of a protein's tertiary structure?

Accepted Answer

Peptide bond hydrolysis

Question 3

A mutation in the gene encoding a protein causes a single amino acid substitution, introducing a hydrophobic patch on the protein surface. Which disease is most likely associated with this type of misfolding?

Accepted Answer

Sickle-cell anemia

Question 4

Which of the following best explains why the protein folding process cannot involve sampling all possible conformations?

Accepted Answer

The number of possible conformations is astronomically large, making random sampling kinetically impossible.

Question 5

Which molecular chaperone system in E. coli is responsible for assisting the folding of proteins that cannot fold spontaneously and involves a double-ring structure capped by a co-chaperone?

Accepted Answer

GroEL/GroES

Question 6

What is the primary role of the hydrophobic effect in protein folding?

Accepted Answer

To drive the burial of nonpolar side chains in the protein core, increasing the entropy of water.

Question 7

Which enzyme catalyzes the interconversion of cis and trans isomers of proline peptide bonds during protein folding?

Accepted Answer

Peptide prolyl cis-trans isomerase (PPI)

Question 8

A patient presents with neurodegenerative symptoms and brain tissue shows spongiform degeneration. Which molecular mechanism is most likely responsible?

Accepted Answer

Accumulation of amyloid fibrils due to misfolded prion proteins.

Question 9

Which of the following statements about the molten globule state in protein folding is CORRECT?

Accepted Answer

It is a compact, partially folded state with secondary structure but flexible side chains.

Question 10

Which of the following best describes the role of Hsp70 in protein folding?

Accepted Answer

It binds to exposed hydrophobic regions of nascent or misfolded proteins, preventing aggregation.

Question 11

Which of the following is a consequence of protein denaturation?

Accepted Answer

The protein loses its functional three-dimensional structure, which may or may not involve complete unfolding.

Question 12

Which of the following is a key difference between amyloidoses and prion diseases?

Accepted Answer

Amyloidoses involve the aggregation of misfolded proteins into amyloid fibrils, while prion diseases involve the infectious propagation of a misfolded protein conformation.

Question 13

Which of the following equations correctly represents the requirement for protein folding to be thermodynamically favorable?

Accepted Answer

$$\Delta G = \Delta H - T\Delta S \u003c 0$$

Question 14

A protein is found to aggregate in the cytoplasm after heat shock. Which cellular system is most likely to be upregulated to prevent this aggregation?

Accepted Answer

Hsp70/Hsp40 chaperone system

Question 15

Which of the following best explains why a deletion of Phe at position 508 in the CFTR protein leads to cystic fibrosis?

Accepted Answer

It results in improper folding and degradation of the CFTR chloride channel.

Question 16

Which of the following is NOT a function of molecular chaperones?

Accepted Answer

Catalyzing peptide bond formation during translation.

Question 17

Which of the following best describes the role of protein disulfide isomerase (PDI) in protein folding?

Accepted Answer

It catalyzes the formation and rearrangement of disulfide bonds to achieve the native conformation.

Question 18

Which of the following is a plausible outcome if a protein fails to fold correctly in the cell?

Accepted Answer

It may be targeted for degradation by the ubiquitin-proteasome system.

Question 19

Which of the following best explains why the conformational entropy change ($$\Delta S) $$upon protein folding is unfavorable?

Accepted Answer

Folding decreases the randomness of the polypeptide chain, reducing entropy.

Protein Folding: Mechanisms, Chaperones, and Disease

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