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Flashcards in Fibrous Proteins_Molecules Deck (38):
1

What are the properties of fibrous proteins?

1) Low solubility
2) No tertiary structure/ no quaternary structure especially collagen, elastin, keratin
3) Mechanical strength/flexibility
4) long chains
5) Twist/coil
6) Cross links: covalent cross links to hold them together

2

Name the keratin diseases

1) Epidermolysis bullosa simplex
2) Junctional epidermolysis bullosa
3) Dystrophic epidermolysis bullosa

3

What is epidermolysis bullies simplex?

- Form of epidermolysis bulls that causes blisters at the site of rubbing
- Autosomal dominant
- Affects keratin genes

4

What is junctional epidermolysis bullosa?

- Inherited disease affecting lamina and collagen
- blister formation within the lamina lucida of the basement membrane zone
- Autosomal recessive
- Blisters at the site of friction

5

What is dystrophic epidermolysis bulls?

- Inherited variant affecting the skin and other organs
- Skin very fragile
- Cause by genetic defect (or mutation) within the human gene encoding protein type VII collagen
- Autosomal dominant or autosomal recessive

6

What does keratin do?

1) Give structural support to epithelial cells
2) Keratin cytoskeleton of dead cells forms hairs, fingernails and the horny layer of skin

7

Keratin is under what class?

One of the several classes of intermediate filaments

8

What do all keratins contain?

Long stretches of alpha helix interrupted by non helical segments.

9

What are the two different types of keratin?

1) Acidic (Type 1)
2) Basic (Type 2)

10

What do they form with type 1 polypeptides?

Heterodimer

11

What do they form with type 2 polypeptides?

A coiled coil

12

How do alpha helices of the two keratins make contact?

through hydrophobic AA side chains on one edge of each helix.

13

What is the structure of keratin

- Protein chains twist in pairs
- Left handed superhelix "coiled coil"
- Hydrophobic faces (facing each other)
- S - S cross links

14

Can the S - S cross links be chemically undone?

Yes
- If it is not there anymore, keratin becomes more flexible
- Adding hydrogen at a warm temperature (using hot water) reduces disulphide bridge

15

What happens to keratin fibres in a high oxidising environment?

H can be removed, allowing covalent links to join keratin fibres by disulphide bond

16

Why is keratin a left handed superhelix

- Pair of twisted alpha helices
- Strongest way is to turn it in the opposite way of the primary helix

17

What type of cross links happen in collagen?

- H bonds (HyPro) - forms cross links by H bonds
- Covalent (Lysinorleucine) - pairs of lysine forms covalent bonds

18

Name the collagen disease

- Scurvy: vitamin C
- Ehlers - Danlos syndrom
- Osteogenesis Imperfecta

19

Most mammals make vitamin C except which mammals?

Humans and Guinea pigs

20

What happens to sailors and Arctic explorers?

Collagen falls apart

21

How many human collagen genes can be affected to cause a collagen disease?

19 human collagen genes

22

What happens in Ehlers-Danlos syndrome?

- Weak connective tissue
- Especially Glycine -> X mutations
- Lethal: fatal in womb
- Minor: Double jointed

23

What happens in osteogenesis imperfect?

- Brittle bones/deformity
- Shortened collagen chains (deletions)
- Sever: Fatal before birth

24

Name the most abundant fibres in strong, tough connective tissue.

Collagen

25

In which connective tissue, is collagen present in?

- Liver
- Aorta
- Bone
- Cartilage
- Cornea
- Skin

26

What is a characteristic of type 1 collagen?

Most unusual amino acid composition
- 35% Glycine
- 21% Proline and hydroxyproline
- 11% Alanine
- 0.6% Hydroxylysine

27

What does hydroxproline need?

Need vitamin C

28

How is glycoprotein made?

Carbohydrate attached at Hydroxylysine

29

What is inorganic bone matrix made of?

Hydroxyapatite

30

What percentage of bone and skin is made of collagen

1/4 bone: Collagen
3/4 skin: Collagen

31

Hydroxylated AA are not represented in the genetic code, therefore...?

Therefore they must be synthesised post translationally from prolyl and lysyl residues in the polypeptide

32

How are collagen chains made?

Three intertwined polypeptide chains in a superhelix

33

What is the unusual polypeptide AA sequence that collagen chains have?

Have glycine in every third position - all glycine residues are on the same side of the helix

34

What are the properties of a collagen helix (one collagen chain)?

- Left handed helix (NOT ALPHA)
- 3 residues/turn
- no H bonds
- held together by steric repulsion of the bulky proline and hydroxyproline side chains

35

What forms the collagen superhelix?

3 left handed helix is turned around in a right handed manner to form the superhelix

36

How is the collagen superhelix superficial structure held together?

By hydrogen bonds between the peptide bonds of the interacting polypeptides

37

How is glycine faced in the collagen superhelix?

Glycine is faced each other in the center of the superhelix.

38

The 3 chains in the superhelix of collagen how many aa long is it? How are they arranged?

>1000 AA long
- Mainly Gly - X - Pro or Gly - X - Hyp (Strictily in this order sequence) [Hyp: hydroxyproline]