Question 1

Which of the following statements best explains why rotation around the peptide bond is restricted, but rotation around the bonds to the α-carbon is permitted?

Accepted Answer

The peptide bond has partial double-bond character due to resonance, restricting rotation, while the bonds to the α-carbon are single bonds and can freely rotate.

$$	ext{O} = 	ext{C} - 	ext{N} \leftrightarrow 	ext{O}^{-} - 	ext{C} = 	ext{N}^{+} \leftrightarrow 	ext{O} = 	ext{C}^{+} - 	ext{N}^{-}$$

Question 2

A protein is found to have a region that is highly enriched in lysine (K), glutamic acid (E), proline (P), and arginine (R). Based on this sequence, what is the most likely structural property of this region?

Accepted Answer

It is likely to be an intrinsically disordered region, capable of adopting multiple conformations depending on binding partners.

Question 3

Which of the following best describes the hydrogen bonding pattern in an α-helix?

Accepted Answer

The carbonyl oxygen of residue $$n$$ forms a hydrogen bond with the amide hydrogen of residue $$n+4.$$

Question 4

A mutation replaces a glycine residue with a valine in the repeating sequence of collagen. What is the most likely consequence at the molecular and organismal level?

Accepted Answer

The triple helix packing is disrupted, leading to weakened connective tissue, as seen in Ehlers-Danlos syndrome.

Question 5

Which of the following best explains why parallel β-sheets are 'slightly weaker' than antiparallel β-sheets?

Accepted Answer

The hydrogen bonds in parallel β-sheets are bent, making them less optimal than the linear hydrogen bonds in antiparallel β-sheets.

Question 6

A patient presents with symptoms of scurvy. Which of the following best describes the molecular mechanism linking vitamin C deficiency to connective tissue breakdown?

Accepted Answer

Vitamin C is required for prolyl hydroxylase activity, which hydroxylates proline in collagen. Without hydroxyproline, collagen triple helices are destabilized, leading to weak connective tissue.

Question 7

Which of the following best describes the first step in protein folding according to the hydrophobic effect?

Accepted Answer

Hydrophobic side chains collapse into the protein interior, minimizing their exposure to water and driving the initial compaction of the polypeptide.

Question 8

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

Accepted Answer

It refers to the arrangement and interaction of multiple polypeptide chains (subunits) in a protein complex.

Question 9

Which of the following best explains why proline is often found at position 2 in Type I β-turns and glycine at position 3 in Type II β-turns?

Accepted Answer

Proline's rigid ring structure induces a sharp turn, while glycine's small size allows for tight packing in the turn.

Question 10

A helical wheel diagram for a peptide shows both glycine and tryptophan residues. What does this suggest about the likelihood of this region forming an α-helix?

Accepted Answer

It is unlikely to form an α-helix, as both glycine and tryptophan are rarely found in α-helices.

Question 11

Which of the following best describes the role of chaperone proteins such as Hsp70/Hsp40 in protein folding?

Accepted Answer

They bind to exposed hydrophobic regions of misfolded proteins, preventing aggregation and allowing refolding.

Question 12

Which of the following is a direct consequence of the partial double-bond character of the peptide bond?

Accepted Answer

The peptide bond is planar and usually adopts a trans configuration.

Question 13

Which of the following best describes the difference between a peptide and a protein, according to the length convention in this chapter?

Accepted Answer

A peptide is generally fewer than 20 amino acids, while a protein (or polypeptide) is longer than that.

Question 14

Which of the following best explains why the GroEL/ES system requires ATP hydrolysis for its function?

Accepted Answer

ATP hydrolysis induces conformational changes in GroEL, allowing the misfolded protein to be encapsulated and refolded within the chamber.

Question 15

A protein with 450 amino acids is synthesized. Using the average residue mass of 110 Da, what is its approximate molecular weight? What is the approximate molecular weight of the mRNA encoding it (assuming 450 codons, no UTRs, and an average ribonucleotide residue mass of 322 Da)?

Accepted Answer

Protein: $$450 	imes 110 = 49,500 Da$$; mRNA: $$450 	imes 3 	imes 322 = 434,700 Da$$

Question 16

Which of the following is a real-world example of how understanding protein structure informs drug design?

Accepted Answer

HIV protease inhibitors are designed to occupy the active site of the viral protease, blocking peptide bond hydrolysis and preventing viral maturation.

Question 17

Which of the following best describes the concept of the protein folding energy funnel?

Accepted Answer

Proteins can follow multiple pathways from the unfolded state to the native state, with the native state representing the lowest energy conformation.

Question 18

Which of the following is a correct statement about the Ramachandran plot?

Accepted Answer

It shows the allowed values of the phi ($$\phi) $$and psi ($$\psi) $$angles for amino acid residues in a protein, with favored regions corresponding to common secondary structures.

Comprehensive Study Notes: Protein Structure and Function (Biochemistry)

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