Question 1

Which of the following best describes the structural organization of α-keratin in hair and nails?

Accepted Answer

Two right-handed α-helices twisted into a left-handed supercoil, stabilized by van der Waals, ionic, and disulfide bonds.

Question 2

Collagen is a major component of connective tissue. Which of the following statements about collagen structure is CORRECT?

Accepted Answer

Collagen consists of three left-handed helices coiled together into a right-handed supercoil.

Question 3

Which amino acid sequence motif is most commonly found in collagen?

Accepted Answer

Gly-Pro-Hyp

Question 4

What is the primary reason for the tight packing of the three chains in the collagen triple helix?

Accepted Answer

The small size of glycine residues at every third position allows close approach of the chains.

Question 5

Which of the following is a direct consequence of vitamin C deficiency in humans?

Accepted Answer

Impaired hydroxylation of proline and lysine residues in collagen, leading to weakened connective tissue.

Question 6

Which of the following interactions is NOT a major stabilizing force in the tertiary structure of globular proteins?

Accepted Answer

Peptide bonds between amino acids.

Question 7

A patient presents with symptoms of scurvy. Which biochemical process is most directly affected?

Accepted Answer

Hydroxylation of proline and lysine residues in collagen synthesis.

Question 8

Which of the following best explains why collagen triple helices are more rigid and less flexible than α-helices?

Accepted Answer

The presence of proline and hydroxyproline residues restricts backbone rotation.

Question 9

Which of the following statements about the heme group in myoglobin is CORRECT?

Accepted Answer

The heme group is a prosthetic group that binds oxygen via an iron atom.

Question 10

Which of the following best describes a protein domain?

Accepted Answer

An independently folded, compact unit within a protein that may have a unique function.

Question 11

Which of the following motifs is commonly found in DNA-binding proteins and is involved in gene regulation?

Accepted Answer

Helix-turn-helix

Question 12

Which of the following statements about supersecondary structure (motifs) is TRUE?

Accepted Answer

Motifs are specific combinations of secondary structure elements that recur in different proteins.

Question 13

A mutation replaces a glycine residue with a bulky amino acid in the collagen triple helix. What is the most likely consequence?

Accepted Answer

Disruption of tight packing, leading to destabilization of the triple helix.

Question 14

Which of the following best explains why humans must obtain vitamin C from their diet?

Accepted Answer

Humans lack the enzyme required to synthesize vitamin C.

Question 15

Which of the following is a function of the hydroxylation of proline and lysine residues in collagen?

Accepted Answer

It aids in the formation and stabilization of the collagen triple helix.

Question 16

Which of the following best describes the role of hydrophobic amino acids in globular proteins?

Accepted Answer

They are typically found in the protein interior, stabilizing the structure by avoiding water.

Question 17

Which of the following is a plausible effect of a defect in the enzyme that hydroxylates proline during collagen synthesis?

Accepted Answer

Formation of unstable collagen fibers, leading to connective tissue disorders.

Question 18

Which of the following best explains the difference between fibrous and globular proteins?

Accepted Answer

Fibrous proteins provide mechanical support and are often insoluble, while globular proteins are soluble and perform diverse functions such as catalysis and transport.

Question 19

Which of the following is a real-life consequence of defective collagen crosslinking in humans?

Accepted Answer

Formation of weak, easily damaged connective tissues.

Question 20

Which of the following best describes the role of prosthetic groups in proteins such as myoglobin?

Accepted Answer

They are non-polypeptide molecules required for the protein's biological activity.

Protein Three-Dimensional Structure: Fibrous and Globular Proteins

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