Protein Targetting

Question 1

What is a collagen?

Answer 1

The most abundant protein in the body

In connective tissue

Question 2

Where is collagen synthesised?

Answer 2

Secreted protein produced by fibroblasts in connective tissue

Question 3

What is the basic structure of collagen?

Answer 3

Tropocollagen
3 polypeptide alpha chains
Triple helix
Glycine in every third position

Question 4

What does collagen structure mean for collagen?

Answer 4

It is non-extensible
Non-compressible
High tensile strength

Question 5

Why is glycine important in collagen?

Answer 5

It is the only amino acid with a side chain small enough to fit in the middle of the helix

Question 6

What is mainly in the X and Y positions of collagen?

Answer 6

Proline and hydroxyproline

Question 7

What bonds connect the three alpha chains?

Answer 7

Hydrogen bonds

Question 8

What is type I collagen and where is it found?

Answer 8

2 alpha I (I) chains and 1 alpha II (I)
Skin, tendons, bone
90% of all collagen

Question 9

What is type II collagen and where is it found?

Answer 9

3 Alpha I (II)

Cartilage and intervertebral discs

Question 10

How is collagen synthesised?

Answer 10

1. Synthesis and then entry into Lumen of rough ER
2. Cleavage of signal peptide
3. Hydroxylation of selected proline and lysine residues
4. Addition of N-linked Oligosaccharides
5. Addition of Galactose to hydroxylysine residues
6. chain alignment and formation of disulfide bonds
7. formation of triple helical pro collagen from C- to N-terminus
8. completion of O linked oligosaccharide chains by addition of glucose
9. transport vesicle
10. Exocytosis
11. Removal of N- and C- terminus propeptides
12. Lateral association of collagen molecules followed by coolant cross linking
    13- Aggregation of fibrils

Question 11

What is Prolyl Hydroxylase?

Answer 11

Allows increased Hydrogen bonding to stabilise triple helix

Requires Vitamin C and Fe2+ for activity

Question 12

What is Scurvy due to?

Answer 12

Lack of vitamin C so Prolyl Hydroxylase will not work so weak tropocollagen triple helix

Question 13

What is Lysyl Oxidase?

Answer 13

Extracellular
Requires Vitamin B6 and Cu2+ ions for activity
Forms covalent cross-links

Question 14

Why is Tropocollagen secreted before final processing occurs?

Answer 14

Too large and would destroy the cell if occurred inside the cell

Question 15

What is EDS?

Answer 15

Ethlers-Danlos Syndrome

Mutation in the Collagen type V or Lysyl Oxidase deficiency