$$(-\text{Gly-Ser-Gly-Ala-Gly-Ala}-)_N$$

$$5.1\ \text{\AA}$$ for $$\alpha$$ keratin, $$5.4\ \text{\AA}$$ for standard $$\alpha$$ helix

Question 1

Which structural protein is depicted in the first image, characterized by extended parallel $$\beta$$ sheets and interdigitating alanine residues?

Accepted Answer

Silk fibroin

Question 2

What is the primary function of ascorbic acid (vitamin C) in collagen biosynthesis?

Accepted Answer

It is required for the hydroxylation of proline residues.

Question 3

Which amino acid is most abundant in collagen, making up approximately one-third of its sequence?

Accepted Answer

Glycine

Question 4

A patient presents with skin lesions, broken blood vessels, and poor wound healing. Which biochemical deficiency is most likely responsible?

Accepted Answer

Deficiency in ascorbic acid (vitamin C)

Question 5

Which structural protein is rich in cysteine and forms disulfide bonds, contributing to its hardness?

Accepted Answer

Hard $$\alpha$$ keratin

Question 6

What is the repeating sequence found in silk fibroin that allows for interdigitation between sheets?

Accepted Answer

$$(-	ext{Gly-Ser-Gly-Ala-Gly-Ala}-)_N$$

Question 7

Which disease is associated with a deficiency in lysine oxidase, resulting in poor collagen crosslinking?

Accepted Answer

Lathyrism

Question 8

What is the structural motif of collagen, and how is it stabilized?

Accepted Answer

Triple right-handed helix composed of left-handed helices stabilized by hydrogen bonds involving hydroxyproline

Question 9

Which structural protein is most likely to be affected in a patient with brittle bones due to a single amino acid substitution?

Accepted Answer

Collagen

Question 10

What is the effect of boiling water on silk cocoons, and which protein remains after this treatment?

Accepted Answer

It removes sericin, leaving fibroin (silk).

Question 11

Which amino acid is responsible for the formation of disulfide bonds in keratin, and how does this affect hair structure?

Accepted Answer

Cysteine; increases hardness and curliness

Question 12

What is the pitch of the $$\alpha$$ keratin helix, and how does it differ from a standard $$\alpha$$ helix?

Accepted Answer

$$5.1\ 	ext{\AA}$$ for $$\alpha$$ keratin, $$5.4\ 	ext{\AA}$$ for standard $$\alpha$$ helix

Question 13

Which protein structure is most associated with mechanical strength in tendons and ligaments?

Accepted Answer

Collagen triple helix

Question 14

Which structural protein is most likely to be affected in a patient with hyperextensible joints and skin (Ehlers-Danlos syndrome)?

Accepted Answer

Collagen

Question 15

What is the role of hydrophobic residues in the coiled-coil structure of $$\alpha$$ keratin?

Accepted Answer

They align to form a hydrophobic strip that stabilizes the dimer interface.

Question 16

Which protein is most likely to lose mechanical integrity in the skin due to mutations, resulting in diseases such as epidermolysis bullosa simplex?

Accepted Answer

Keratin

Question 17

Which protein is composed of a triple helix with a repeating Gly-X-Y sequence, where X is often proline and Y is often hydroxyproline?

Accepted Answer

Collagen

Question 18

What is the effect of inhibiting lysine oxidase on collagen structure?

Accepted Answer

Collagen fails to crosslink, resulting in weak connective tissue.

Question 19

Which protein is most likely to be hydrolyzed by cocoonase in adult moths, facilitating their escape from cocoons?

Accepted Answer

Silk fibroin and sericin

Question 20

Which structural protein is most associated with the ability to stretch and then return to its original shape, due to its helical structure?

Accepted Answer

Keratin

Structural Proteins: Keratin, Silk, and Collagen

Study Guide - Practice Questions