$$\text{Gly-X-Y}$$, where X is often proline and Y is often hydroxyproline

Question 1

Which of the following is a key biochemical property shared by all fibrous proteins?

Accepted Answer

They have limited sequence variation and are composed of long, extended chains.

Question 2

The high tensile strength of collagen is primarily due to which structural feature?

Accepted Answer

The triple helix structure formed by three left-handed helices coiling into a right-handed superhelix.

Question 3

A patient presents with symptoms of scurvy, including weak connective tissue and bleeding gums. Which biochemical process is most directly impaired?

Accepted Answer

Hydroxylation of proline and lysine residues in collagen due to vitamin C deficiency.

Question 4

Which amino acid is most abundant in silk fibroin, contributing to its ability to form stacked $$\beta-$$sheets?

Accepted Answer

Glycine

Question 5

The hardness of $$\alpha-$$keratin, such as in rhinoceros horn, is primarily due to:

Accepted Answer

A high percentage of amino acids cross-linked by disulfide bonds.

Question 6

Which process occurs during a 'permanent' hair treatment at a salon?

Accepted Answer

Disulfide bonds in $$\alpha-$$keratin are broken and reformed in new positions, resulting in curled hair.

Question 7

Which repeating sequence is characteristic of collagen?

Accepted Answer

$$	ext{Gly-X-Y}$$, where X is often proline and Y is often hydroxyproline

Question 8

Which of the following best explains why glycine is essential in the collagen triple helix?

Accepted Answer

Glycine's small side chain allows it to fit into the crowded interior of the triple helix.

Question 9

Which enzyme catalyzes the hydroxylation of proline and lysine in collagen, and what cofactor is required?

Accepted Answer

Prolyl hydroxylase; ascorbic acid (vitamin C)

Question 10

A mutation replaces glycine with valine in the collagen sequence. What is the most likely consequence?

Accepted Answer

Disruption of the triple helix due to steric hindrance, leading to weaker connective tissue.

Question 11

Which structural feature is unique to silk fibroin compared to $$\alpha-$$keratin and collagen?

Accepted Answer

Antiparallel $$\beta-$$sheets stabilized by hydrogen bonds between backbone NH and CO groups.

Question 12

Which of the following best describes the organization of $$\alpha-$$keratin fibers?

Accepted Answer

Right-handed $$\alpha-$$helices form left-handed coiled-coils, which assemble into protofilaments and then into protofibrils.

Question 13

Which amino acids are most prevalent in $$\alpha-$$keratin, contributing to its hydrophobic core?

Accepted Answer

Ala, Val, Leu, Ile, Met, Phe

Question 14

What type of covalent cross-link forms between collagen triple helices, increasing tissue strength?

Accepted Answer

Schiff base between allysine and lysine residues

Question 15

Which property of silk fibroin allows it to be both strong and elastic?

Accepted Answer

Crystalline $$\beta-$$sheet regions connected by amorphous regions

Question 16

A scientist is designing a synthetic fiber with high tensile strength and elasticity. Which combination of protein features should they mimic?

Accepted Answer

Stacked $$\beta-$$sheets with alternating small side chains and amorphous regions, as in silk fibroin

Question 17

Which of the following statements about fibrous proteins is FALSE?

Accepted Answer

They are highly soluble in water due to their hydrophilic amino acids.

Question 18

Which real-world scenario best illustrates the importance of collagen cross-linking?

Accepted Answer

Elderly individuals with reduced collagen cross-linking experience weaker bones and increased risk of fractures.

Question 19

Which of the following is NOT a role of $$\alpha-$$keratin in organisms?

Accepted Answer

Providing elasticity in tendons

Fibrous Proteins: Structure, Properties, and Biological Roles

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