Question 1

Which of the following statements best describes the role of prosthetic groups in globular proteins?

Accepted Answer

They are small molecules that may be noncovalently or covalently bonded to the protein and are essential for the protein's function, such as heme in myoglobin.

Question 2

A protein domain is typically defined as:

Accepted Answer

A compact, independently folding unit of a protein, often around 200 amino acids, that may possess a specific function.

Question 3

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

Accepted Answer

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

Question 4

Which of the following conditions is most likely to cause protein denaturation?

Accepted Answer

Exposure to organic solvents or urea.

Question 5

What is the main thermodynamic driving force for the folding of globular proteins?

Accepted Answer

Favorable gain of solvent entropy due to the hydrophobic effect.

Question 6

Which amino acid is most commonly found in turns and bends of globular proteins, and why?

Accepted Answer

Proline, because its cyclic structure introduces kinks and cannot act as an H-bond donor.

Question 7

Which of the following statements about protein folding is supported by Anfinsen's experiment with ribonuclease A?

Accepted Answer

The information required for a protein to fold into its native structure is contained in its amino acid sequence.

Question 8

Disulfide bonds contribute to protein stability primarily by:

Accepted Answer

Reducing the number of possible conformations in the unfolded state, thus decreasing conformational entropy.

Question 9

Which of the following is a correct description of the 'molten globule state' in protein folding?

Accepted Answer

A compact, partially folded state with native-like secondary structure but not fully formed tertiary interactions.

Question 10

Which enzyme catalyzes the isomerization of prolyl bonds during protein folding?

Accepted Answer

Peptide prolyl isomerase.

Question 11

Chaperones are especially important in cells under stress because:

Accepted Answer

They prevent intermolecular interactions that lead to protein aggregation.

Question 12

Which of the following best describes the function of the GroEL-GroES chaperonin system?

Accepted Answer

It undergoes a conformational change upon ATP and GroES binding, presenting a hydrophilic interior that promotes proper folding.

Question 13

Amyloid fibrils are associated with several human diseases because:

Accepted Answer

They result from ordered aggregation of misfolded proteins, leading to diseases such as Alzheimer's and prion diseases.

Question 14

Which of the following equations correctly represents the change in Gibbs free energy ($$\Delta G) $$for protein folding?

Accepted Answer

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

Question 15

A protein is found to have a highly twisted beta-sheet structure forming a barrel. This structural motif is most likely to:

Accepted Answer

Contribute to the formation of a channel or pore in membranes.

Question 16

Which of the following is NOT a typical denaturing condition for proteins?

Accepted Answer

Formation of native disulfide bonds.

Question 17

Which of the following statements about the energy landscape of protein folding is correct?

Accepted Answer

The energy landscape is often rugged, with multiple intermediates and possible off-pathway states.

Question 18

Which process is catalyzed by protein disulfide isomerases during protein folding?

Accepted Answer

Reduction and reoxidation of disulfide bonds to correct non-native disulfide formation.

Question 19

Which of the following is a consequence of burying hydrophobic groups in the interior of a globular protein?

Accepted Answer

Release of ordered water molecules, increasing solvent entropy.

Question 20

A mutation replaces a surface-exposed hydrophilic residue in myoglobin with a hydrophobic one. What is the most likely effect?

Accepted Answer

Decreased solubility and possible aggregation due to exposure of hydrophobic groups.

Chapter 6.3

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