Chapter 4: 4.2 Macromolecules: Fibers

Question 1

Describe:

Silk fibers structure

Answer 1

Beta sheets consisting of repeating units:
* - [Gly-Ser-Gly-Ala-Gly-Ala]n -

Question 2

What does the structure of silk fibers allow for?

Answer 2

• Small residues allow for tight packing and the beta sheets prevent stretch

Question 3

True or False:

Silk Fibers are not resistant to tension as they cannot stretch

Answer 3

False, the fibers are strong and resistant to tension

Question 4

Describe:

Keratins

Answer 4

Fibers consisting of alpha-helices (contain alanine and glutamine) and cystine cross links
* Helices consist of 7 amino acid repeats

Question 5

What contains keratin?

Answer 5

• Hair
• Wool
• Skin
• Horns
• Claws
• Hooves

Question 6

True or False:

Keratin can be classified as hard or soft

Answer 6

True

Question 7

How can keratins be defined as hard or soft?

Answer 7

Based on sulfur content

Question 8

Keratins like wool are very ——–

Answer 8

Stretchy

Question 9

Describe:

What happens to keratins like wool when stretched?

Answer 9

When stretched the H-bonds found within the α-helix strands can be broken allowing adjacent strands to form β-sheet H-bonds

Question 10

How can wool resume shape?

Answer 10

Due to cystine cross links

Question 11

Define:

Collagen

Answer 11

The most abundant protein in the human body
* Makes up skin tendons, and bones

Question 12

Describe:

Collagen structure

Answer 12

A triple helix quarternary structure
* Three amino acid chains intertwined
* Each amino acid chain has a “poly-proline type II” secondary structure
* Every third amino acid is glycine
* Hydroxy-proline stabilizes the triple helix by forming hydrogen bonds between the three amino acid chains

Question 13

Describe:

Poly-proline type II helices

Answer 13

• More stretched out than the alpha-helix
• The helix is held together by repulsion between the proline side chains

Question 14

Describe:

Glycine’s role collagen

Answer 14

Allows the triple helix to form because it is the only amino acid with a side chain small enough to fit in the center of the helix

Question 15

Describe:

Function of Hydroxy-lysine

Answer 15

Involved in forming cross-links between the collagen strands to stabilize the collagen fibril

Question 16

Define:

Hydroxy-proline

Answer 16

Proline with an -OH group

Question 17

Define:

Hydroxy-lysine

Answer 17

Lysine with an -OH group

Question 18

List:

3 collagen-related diseases

Answer 18

• Scurvy
• Osteogenesis imperfecta
• Ehlers-Danlos syndrome

Question 19

Define:

Scurvy

Answer 19

Lack of Vitamin C
* Needed by the enzyme that hydroxylates proline, creates unstable collagen

Question 20

Define:

Osteogenesis imperfecta

Answer 20

Glycine mutations lead to a lack of collagen
* Leads to malformed or absent bones

Question 21

Define:

Ehlers-Danlos syndrome

Answer 21

Mutations in the collagen gene
* Inherited connective tissue disorder