Biochemistry of the Periodontal Ligament in Health and Disease Flashcards
1
Q
What is the origin of all connective tissues?
A
Mesodermal origin
2
Q
Give an example of a connective tissue in the periodontium?
A
The periodontal ligament
3
Q
Give a generic function description of the function of connective tissue
A
Binding / connecting other tissue systems (such as muscle to skin) or organs
4
Q
What are connective tissues made up of?
A
Nerves
Blood vessels
Cells
The extracellular matrix (ECM) that surrounds these cells and in to which they are embedded
5
Q
What can the extracellular matrix be further divided into?
A
- The fibrous components
2. The “Cement” surrounding these fibres.
6
Q
What is the “Cement” division of the ECM called?
A
The ground substance
7
Q
What can the fibrous component of connective tissue be divided into?
A
Sub-divided in to major and minor fibres, according the size of their fibre diameters.
8
Q
Name some of the cells found in the PDL
A
Fibroblasts
Cementoblasts
Osteoblasts
9
Q
Give an example of the major fibres found in the ECM
A
Collagen
10
Q
Give an example of the minor fibres found in the ECM
A
Oxytalan
Elastin
11
Q
What makes up 3% of the ECM?
A
The minor fibres
12
Q
What do elastic fibres do in connective tissues?
A
They provide elasticity to the tissue
13
Q
What are mature elastic fibres made up of?
A
2 components:
- Microfibrillar component
- Inner core (or the filling)
14
Q
Describe the microfibrillar component of mature elastic fibres
A
It is an external tube like structure in the elastic fibre
15
Q
Describe the Inner core component of mature elastic fibres
A
It is the “filling”, made up of an amorphous polymeric protein called elastin
16
Q
How much of the mature elastic fibre is made up of elastin protein?
A
90%
17
Q
Name the minor fibres in the PDL in increasing level of maturity
A
Oxytalan
Elaunin
Elastin
18
Q
What do most mature connective tissues have in their ECM?
A
Elastin fibres
19
Q
What are elastin fibres made up of?
A
Microfibrillar protein plus its elastin core
20
Q
Describe elastin fibres in the developing foetus
A
When an elastin fibre is first developing in foetal connective tissues, only the microfibrillar component is present – there is no elastin protein filling until later, when the tissue matures.
21
Q
What are the microfibrillar fibres at the foetal stage called?
A
Oxytalan fibres
22
Q
What are immature elastin fibres called?
A
Oxytalan fibres
23
Q
What happens as the connective tissue begins to mature in regards to minor fibres
A
Elastin protein is deposited within the microfibrillar network to start to produce fibres more similar to those we see in mature tissues. At this intermediate stage, the fibres are known as “elaunin fibres”.
24
Q
How are minor fibres in the PDL different to other connective tissues?
A
Oxytalan fibres are present in periodontal ligament and some elaunin has been reported but no mature elastin fibres in the PDL
25
What is the major fibrous component of connective tissues?
COLLAGEN
26
What do collagen fibres look like under the microscope?
Collagen fibrils have a characteristic striped or banded appearance.
27
What is the periodontium?
The Molex tissues that attaches to the tooth to the jaw
28
What are 4 components of the periodontium?
1. Alveolar bone
2. Cementum
3. Periodontal ligament
4. The gingiva
29
What are all types of connective tissues made up of?
1. Cells
| 2. A grond substance or extracellular matrix
30
What is the ground substance?
Ground substance is a jelly like substance that contains fibres, cells vascular tissue and nerves
31
When does the ground substance become extracellular matrix?
When the jelly like pool combines with fibres that form the tissue
32
What cells can be found in the PDL?
Fibroblasts
cementoblasts
Osteoblasts
33
What do fibroblasts do?
Form all the collagen fibres and secretes enzyme that degrades them
34
What do cementoblasts do?
Forms the cementum
35
What do the minor fibres make up in the PDL?
3% Of the extra cellular matrix
36
Name the 3 main minor fibres in increasing order of maturity
Oxytalan
Elaunin
Elastin
37
What are elastic fibres mainly formed of?
A micro fibrillar coat and a protein core
38
Describe the protein core of young elastin fibres
The protein core is smaller in younger fibres
39
Describe oxytalan
They are immature minor fibres
| They are only made up of the microfibrilar coat it is hollow without a protein core
40
What happens to oxytalan as the tissue matures?
Protein begins to deposit inside the microfibrilar coat until the core is no longer hollow
41
What is matured oxytalan called?
elaunin
42
What is mature elaunin called?
Elastin
43
Which minor fibres make up the PDL?
Oxytalan and elaunin
44
Which minor fibre is NOT found in the PDL?
Elastin
45
The fact that the PDL doesn't contain any mature elastin shows what?
It maintains some embryonic characters
46
Which type of collagen is most abundant in the body?
Type 1 collagen
47
What are all types of collagen made up of?
of 3 polypeptide chains, each called a collagen alpha chain
48
How many different types of collagen fibres are there?
12 TYPES
49
Which type of collagen predominantly makes up the PDL?
Type 1 (80% of all collagen fibres in the PDL are type 1)
50
Name the types of collagen that made up the PDL
```
Type 1 (80%)
Type 3 (20%)
```
51
Name the percentage of type 3 collagen found in mature, embryonic and PDL connective tissues
Mature: 10%
Embryonic: 30%
PDL: 20%
52
Name the structure of collagen type 1
Triple helical structure (braid like structure)
53
What is collagen type one made up of?
3 Polypeptide alpha chains that wind around each other to form a triple helical structure
54
Describe the 3 polypeptide chains that make up collagen type 1
2 are alpha 1 chains
| 1 is an alpha 2 chain
55
What is one unit of collagen called?
Tropocollagen
56
What is the structure of the polypeptide chains
Each poly peptide chain has an overall repeating tri-peptide structure of glycine (GLY) followed by proline/hydroxyproline and then alanine
57
Name the 3 peptides that form the polypeptide chain that forms type 1 collagen
Glycine- Proline/hydroxyproline- Alanine
| Usually this is the structure
58
What would we see if we were to look down at a cross section of a single type 1 collagen molecule?
We would see that the glycine is facing the middle while the other 2 amino acids are facing outwards
59
Why does glycine appear to be facing the middle when we look at a cross section of a single type 1 collagen molecule?
As glycine is has a small side chain which can easily fit without steric hindrance
60
What is th importance of glycine facing the middle in a cross section of a single type 1 collagen molecule?
Glycine forms hydrogen bonds between the 3 poly peptide chains making sure the triple helical structure of collagen is stable
61
What would the consequence be of a mutated glycine molecule in collagen?
Leads to instability of the triple helical compound and as a result instability of collagen type 1 fibres
This happens in one of the forms of osteogenesis imperfecta
62
What is osteogenesis imperfecta?
The brittle bone disease
| Due to a mutation in glycine resulting in unstable collagen type 1
63
Name all the types of collagen that make up fibres
```
Type I
Type II
Type III
Type V
Type XI
```
64
Where is type I collagen found?
Bone, dentine, skin, tendon, ubiquitous except in cartilage
65
Where is type III collagen found?
It is Co-expressed with Type I, varies with age in different tissues. Foetal skin, blood vessels
66
How does proline turn into hydroxyproline?
By the proline hydroxylase enzyme
67
What proline hydroxylase enzyme need to work?
Vitamin C
68
Why is the hydroxylation of proline important?
it is important in the boning and therefore In maintaining the stability of collagen
69
What disease can occur due to lack of vitamin C?
Scurvy (vascular fragility)
70
Which cell is reasonable for collagen secretion?
Fibroblasts
71
What is pro collagen?
Pre cursors of collagen
72
Describe the process of collagen formation
1. Individual alpha chains for type I collagen are produced at the ribosomes
2. The alpha chains come to the C terminal in a globular form
3. the triple helix of Type I collagen forms spontaneously
4. Sugars are added in the RER and Golgi
to form a glycoprotein
5. Secreted outside the cells
73
What is the importance of the individual alpha chains forming a globular protein structure at the C terminal?
To secure the triple helical structure and to prevent the chains forming fibrils
74
What stabilises the tropocollagen molecule?
disulphide bonds that form across the three chains at the carboxyl terminals
75
Why can't pro collagen molecules form fibres?
because of the globular extensions, called pro-peptides, at either end
76
How do procollagen fibres become able to form fibres?
Once outside the cell, enzymes called propeptidases cleave off the globular extensions, leaving the triple helical collagen molecule free to assemble in to collagen fibres.
77
What do Pro-peptides prevent in pro collagen molecules?
Pro-peptides prevent intracellular aggregation of collagen.
78
What are pro collagen molecules without the Pro-peptides called?
Tropocollagen
79
What would happen if the enzyme propeptidases is missing?
Collagen type 1 will not form fibres and so there wont be strong crosslinked structres in the body
Lethal
80
What happens once the Pro-peptides are removed in pro collagen?
individual triple helical tropocollagen molecules will spontaeously assemble in to aggregate structures
81
How does the aggregation of tropocollagen occur?
in a highly ordered fashion
| one individual tropcollagen moves by three quarter of its length from the tropcollagen next to it.
82
How far are the bands in the PDL ?
65nm
83
What causes the bad like appearance of collagen fibres?
The highly repetitive organised assembly of tropocollagen
84
What is found between rows of tropocollagen?
Cross linking bonds
85
What s the crosslink of collagen
It is intermolecular cross links formed between individual tropocollagen molecules
86
Why do crosslinks form in collagen?
Due to the conversion of lysine and hydroxylysine into their aldehyde forms
87
How do lysine and hydroxylysine get converted into their aldehyde forms?
By an extracellular enzyme: Lysyl oxidase
88
What does Lysyl oxidase do?
It converts the side chains (R groups) on some lysine and hydroxylysine residues to their aldehyde forms
89
What is Lysyl oxidase dependent on?
Lysly oxidase is copper dependent
90
What makes lysyl oxidase unusual?
It is unusual in its ability to be able to be active on proteins that are present within fibrillar structures rather than being free.
91
What is the aldehyde form of the lysine side chain called?
Allysine
92
What is the aldehyde form of the hydroxylysine side chain called?
hydroxyallysine
93
Are crosslinks permanent?
No they are strong but they can be reduced
94
What happens once the aldehyde form of lysine and hydroxylysine have formed?
They will go on to form stable covalent cross links between collagen molecules within the fibrils
95
Which 2 cross linkages are the most important?
DHLN
| HLN
96
Why are cross links reducible in the PDL
They are cleaved during the turnover of the collagen
97
What does turnover of the collagen mean?
When the collagen is degraded and renewed
98
Where are non reducible cross links found?
In almost all mature connective tissues with increasing age
| EG skin
99
Describe non reducible cross links
They form with age and are very stable
| They cannot be broken even in a lab
100
What is the ratio of DHLNL:HLNL in the periodontal ligament
1.3
101
Summarise the biosynthesis of collagen type 1
1. Synthesis of individual pro alpha chains at the RER
2. Hydroxylation of PRO & LYS (Require vitamin C)
3. Glycosylation of HYL and ASN
4. Alignment of pro α chains (disulphide bonds form)
5. PROCOLLAGEN TRIPLE HELIX forms
6. Golgi (more glycosylation)
7. Molecule moves out of cell
8. Cleavage of terminal propeptides
9 TROPOCOLLAGEN forms
10. Aggregation, ¾ stagger array
11. Formation of intermolecular crosslinks using Lysyl
oxidase
12. Fibrils form
13. Fibres form
102
List the hierarchy of type 1 collagen?
1. Procollagen (intracellular)
2. Tropocollagen
3. Microfibrils
4. Fibrils
5. Fibres
6. Fibre bundles
103
How is collagen broken down?
By an enzyme called collagenase
104
Which cells secrete collagenase?
Fibroblasts and by cells associated by inflammation and innate defence like polymorphonucleocytes
105
What family is collagenase part of?
Belongs to a family of enzymes known as matrix metalloproteases, or MMPs.
106
Describe the ideal conditions for collagenase to work at?
Neutral pH optimum
Contain Zn++
Endopeptidase
Require Ca++
107
What form do cells secrete collagenase as?
Cells produce collagenases as inactive precursors that are self activated after secretion
108
How are collagenases turned off after being active?
are turned off by binding to a small peptide, called Tare turned off by binding to a small peptide, called TIMP (tissue inhibitor of metalloproteases)
109
What is TIMP (tissue inhibitor of metalloproteases) produced by?
Cells
110
What does TIMP synthesisregulate?
TIMP synthesis will regulate collagen degradation within a tissue.
111
What type of enzyme is collagenas?
It is an endopeptidase, cleaving collagen molecules within their length in to three quarter and one quarter length fragments.
112
What is Allysine?
The aldehyde form of the lysine side chain
113
What does TIMP (tissue inhibitor of metalloproteases) do?
Turns off the collagen
114
What is hydroxyallysine?
The aldehyde form of the hydroxylysine side chain
