Question 1

Which of the following best describes the arrangement of side chains in a β-strand?

Accepted Answer

Side chains alternate above and below the plane of the strand.

Question 2

In an antiparallel β-sheet, what is the primary difference in hydrogen bonding compared to a parallel β-sheet?

Accepted Answer

Hydrogen bonds are more linear and thus stronger in antiparallel β-sheets.

Question 3

Which amino acid is most commonly found at the position where β-strands cross in the collagen triple helix, and why?

Accepted Answer

Glycine, because its small side chain allows close packing of the three chains.

Question 4

A mutation in the gene encoding prolyl-4-hydroxylase leads to a deficiency in 4-hydroxyproline. What is the most likely consequence for collagen structure?

Accepted Answer

Collagen will denature at a lower temperature, leading to weaker connective tissue.

Question 5

Which of the following best explains why hydrophobic residues are typically found in the interior of globular proteins?

Accepted Answer

The hydrophobic effect drives nonpolar side chains to the protein core to maximize entropy of water.

Question 6

Which of the following is a characteristic feature of the α/β barrel motif?

Accepted Answer

It consists of alternating α-helices and β-strands arranged in a closed barrel structure.

Question 7

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

Accepted Answer

Hydroxylation of proline residues in collagen by prolyl-4-hydroxylase.

Question 8

Which of the following statements about β-turns is correct?

Accepted Answer

β-turns always involve four amino acids and often include glycine or proline.

Question 9

Keratin is a fibrous protein with a coiled-coil structure. What is the primary stabilizing interaction between the two α-helices in the coiled coil?

Accepted Answer

Hydrophobic interactions between residues at positions a and d of the heptad repeat.

Question 10

Which of the following best describes the role of vitamin C in collagen biosynthesis?

Accepted Answer

Vitamin C acts as a cofactor for prolyl-4-hydroxylase, preventing its oxidation and allowing hydroxylation of proline.

Question 11

A globular protein is found to have a hydrophobic core and a hydrophilic surface. Which thermodynamic parameter is most directly associated with this arrangement?

Accepted Answer

$\Delta G < 0$ due to the hydrophobic effect maximizing entropy of water.

Question 12

Which of the following is NOT a typical feature of fibrous proteins?

Accepted Answer

They are soluble in water and have a compact globular shape.

Question 13

Which of the following best describes the difference between secondary and tertiary protein structure?

Accepted Answer

Secondary structure involves local folding patterns stabilized by hydrogen bonds, while tertiary structure is the overall 3D folding of a single polypeptide chain.

Question 14

Which of the following motifs is commonly found in globular proteins and consists of a repeating pattern of β-strands and α-helices?

Accepted Answer

α/β barrel

Question 15

A protein domain is best defined as:

Accepted Answer

A compact, independently folded unit within a polypeptide chain that often has a specific function.

Question 16

Which of the following statements about the collagen triple helix is correct?

Accepted Answer

It consists of three left-handed helices wrapped around each other to form a right-handed superhelix.

Question 17

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

Accepted Answer

It contains tightly packed antiparallel β-sheets stabilized by dispersion forces between small side chains.

Question 18

Which of the following amino acids is most likely to be found in a β-turn, and why?

Accepted Answer

Glycine, because its small size allows tight turns.

Question 19

A protein is found to have both α-helices and β-sheets in its structure. Which level of protein structure does this describe?

Accepted Answer

Tertiary structure

Question 20

Which of the following is a direct consequence of the hydrophobic effect in protein folding?

Accepted Answer

Nonpolar side chains are buried in the protein core, increasing the entropy of surrounding water molecules.

Protein Secondary Structure: β-Strands, β-Sheets, and Connecting Motifs

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