Question 1

Which of the following statements best describes the structural role of fibrous proteins in animal tissues?

Accepted Answer

They provide mechanical strength and structural support due to their elongated, filamentous forms and well-defined secondary structures.

Question 2

Which amino acid is most abundant in silk fibroin, and what structural feature does this confer?

Accepted Answer

Glycine; it allows close packing of antiparallel $\beta$-sheets due to its small side chain.

Question 3

The repeating sequence motif in collagen is $	ext{Gly-X-Y}$, where X and Y are often which amino acids?

Accepted Answer

X is proline and Y is proline or hydroxyproline.

Question 4

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

Accepted Answer

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

Question 5

Which structural feature distinguishes $\alpha$-keratin from collagen?

Accepted Answer

$\alpha$-keratin is predominantly $\alpha$-helical and forms coiled-coil structures, while collagen consists of left-handed helices forming a right-handed triple helix.

Question 6

Which process contributes to the increasing brittleness of collagen fibers as animals age?

Accepted Answer

Accumulation of cross-links formed by oxidation of lysine side chains to aldehydes, followed by aldol condensation and dehydration.

Question 7

Which of the following best explains why every third residue in collagen must be glycine?

Accepted Answer

Glycine's small side chain allows the close packing of the three polypeptide chains in the triple helix.

Question 8

Which of the following is a correct description of the secondary structure found in silk fibroin?

Accepted Answer

Antiparallel $\beta$-sheets with repetitive sequences rich in glycine and alanine.

Question 9

Which amino acid is most responsible for the elasticity of collagen fibers?

Accepted Answer

Hydroxyproline, due to its ability to form hydrogen bonds between chains.

Question 10

A mutation replaces glycine with valine in the Gly-X-Y motif of collagen. What is the most likely consequence?

Accepted Answer

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

Question 11

Which of the following best describes the assembly process of $\alpha$-keratin intermediate filaments?

Accepted Answer

Monomers pair via a parallel coiled-coil to form dimers, which then associate into protofilaments and protofibrils.

Question 12

Which of the following is NOT a major fibrous protein found in animal tissues?

Accepted Answer

Hemoglobin

Question 13

Why is vitamin C essential for healthy connective tissue?

Accepted Answer

It acts as a cofactor for the hydroxylation of proline and lysine residues in collagen, stabilizing the triple helix.

Question 14

Which of the following amino acids is most abundant in $\alpha$-keratin and contributes to its structural stability?

Accepted Answer

Cysteine, which forms disulfide bonds.

Question 15

Which structural feature of silk fibroin allows it to be both strong and flexible?

Accepted Answer

Alternating regions of close-packed $\beta$-sheets and compact folded regions.

Question 16

Which of the following best explains the mechanical properties of fibrous proteins?

Accepted Answer

Their amino acid sequences favor specific secondary structures that confer strength, flexibility, or elasticity.

Question 17

Which process occurs in the endoplasmic reticulum during collagen synthesis?

Accepted Answer

Hydroxylation of proline and lysine residues.

Question 18

Which of the following is a consequence of increased cross-linking in collagen fibers with age?

Accepted Answer

Collagen becomes less elastic and more brittle.

Question 19

Which of the following best describes the role of hydroxylysine in collagen?

Accepted Answer

It is involved in cross-linking between collagen molecules, contributing to tensile strength.

Question 20

Which of the following is a correct statement about the secondary structure of $\alpha$-keratin?

Accepted Answer

It is built on a coiled-coil $\alpha$-helical structure.

Chapter 6.2

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