biochem1 Flashcards
What is the origin of all connective tissues?
Mesodermal origin
Give an example of a connective tissue in the periodontium?
The periodontal ligament
Give a generic function description of the function of connective tissue
Binding / connecting other tissue systems (such as muscle to skin) or organs
What are connective tissues made up of?
Nerves Blood vessels Cells The extracellular matrix (ECM) that surrounds these cells and in to which they are embedded
What can the fibrous component of connective tissue be divided into?
Sub-divided in to major and minor fibres, according the size of their fibre diameters.
Give an example of the major fibres found in the ECM
Collagen
Give an example of the minor fibres found in the ECM
Oxytalan| Elastin
What makes up 3% of the ECM?
The minor fibres
What do elastic fibres do in connective tissues?
They provide elasticity to the tissue
What are mature elastic fibres made up of?
2 components:
1. Microfibrillar component (10%)
2. Inner core (or the filling) 90%
Describe the microfibrillar component of mature elastic fibres
It is an external tube like structure in the elastic fibre
Describe the Inner core component of mature elastic fibres
It is the “filling”, made up of an amorphous polymeric protein called elastin
How much of the mature elastic fibre is made up of elastin protein?
90%
Name the minor fibres in the PDL in increasing level of maturity
Oxytalan > Elaunin > Elastin
What do most mature connective tissues have in their ECM?
Elastin fibres
What are elastin fibres made up of?
Microfibrillar protein plus its elastin core
Describe elastin fibres in the developing foetus
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.
What are the microfibrillar fibres at the foetal stage called?
Oxytalan fibres
What are immature elastin fibres called?
Oxytalan fibres
What happens as the connective tissue begins to mature in regards to minor fibres
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”.
How are minor fibres in the PDL different to other connective tissues?
Oxytalan fibres are present in periodontal ligament and some elaunin has been reported but no mature elastin fibres in the PDL
What is the major fibrous component of connective tissues?
COLLAGEN
What do collagen fibres look like under the microscope?
Collagen fibrils have a characteristic striped or banded appearance.
What is the periodontium?
tissues that attaches to the tooth to the jaw
What are 4 components of the periodontium?
AV bone, cementum (calcified)
PDL, lamina propria of gingiva (non-calcified)
What are all types of connective tissues made up of?
- Cells| 2. A grond substance or extracellular matrix
What is the ground substance?
Ground substance is a jelly like substance that contains fibres, cells vascular tissue and nerves
When does the ground substance become extracellular matrix?
When the jelly like pool combines with fibres that form the tissue
What do fibroblasts do?
Form all the collagen fibres and secretes enzyme that degrades them
Describe the protein core of young elastin fibres
The protein core is smaller in younger fibres
Describe oxytalan
They are immature minor fibres. They are only made up of the microfibrillar coat it is hollow without a protein core
What happens to oxytalan as the tissue matures?
Protein begins to deposit inside the microfibrilar coat until the core is no longer hollow
What is matured oxytalan called?
elaunin
What is mature elaunin called?
Elastin
Which minor fibres make up the PDL?
Oxytalan and elaunin
Which minor fibre is NOT found in the PDL?
Elastin
The fact that the PDL doesn’t contain any mature elastin shows what?
It maintains some embryonic characters
Which type of collagen is most abundant in the body?
Type 1 collagen
What are all types of collagen made up of?
of 3 alpha polypeptide chains, 2 similar (alpha-1), 1 diff (alpha-2) that braid together to form a triple helical structure, which is one molecule of collagen, called a tropocollagen.
Which type of collagen predominantly makes up the PDL?
Type 1 (80% of all collagen fibres in the PDL are type 1)
Name the types of collagen that made up the PDL
Type 1 (80%)Type 3 (20%)
Name the percentage of type 3 collagen found in mature, embryonic and PDL connective tissues
Mature: 10% Embryonic: 30% PDL: 20%
hence, PDL is more immature rather than mature (it does not mature over time)
Name the structure of collagen type 1
Triple helical structure (braid like structure)
What is the structure of the polypeptide chains
repeating tri-peptide structure of glycine (GLY) followed by proline/hydroxyproline and then alanine
[-GLY-PRO-ALA] or [-GLY-HYP-ALA-]
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
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
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
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
What is osteogenesis imperfecta?
The brittle bone disease| Due to a mutation in glycine resulting in unstable collagen type 1
Where is type I collagen found?
Bone, dentine, skin, tendon, ubiquitous except in cartilage
Where is type III collagen found?
It is Co-expressed with Type I, varies with age in different tissues. Foetal skin, blood vessels
How does proline turn into hydroxyproline?
By the proline hydroxylase enzyme
What proline hydroxylase enzyme need to work?
Vitamin C
What disease can occur due to lack of vitamin C?
Scurvy (vascular fragility)
Which cell is reasonable for collagen secretion?
Fibroblasts
procollagen vs tropocollagen?
pro= pre-cursor of collagen, inside the cell. cut off the globular proteins (pro peptides) and u get..
tropo= outside the cell
Describe the process of collagen formation
- Individual separated alpha chains for type I collagen are produced at the ribosomes in the RER
- The alpha chains come to the C terminal in a globular form like a hair tie- called pro peptide. (proteins have N amine terminal and C carbon terminal NCC)
- the chains link together w disulphide bonds, which regulate the collagen to start braiding the triple helicase structure.
- when done, another globular protein (pro peptide), hair tie is added at the bottom to hold THS together.
- procollagen is secreted outside, into extracellular matrix, and pro peptides are cut off, leaving tropocollagen to join w other tropos and form collagen fibrils.
What is the importance of pro peptides (hair ties)
stop procollagen forming fibrils, we don’t want this intracellular aggregation of collagen inside the cell, wanna prevent this until tropocollagen is secreted outside the cell
What stabilises the tropocollagen molecule?
disulphide bonds that form across the three chains at the carboxyl terminals
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.
What are pro collagen molecules without the Pro-peptides called?
Tropocollagen
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 bodyLethal
How does the stagger aggregation of tropocollagen occur?
in a highly ordered fashion
one individual tropcollagen moves by 3/4 of its length from the tropcollagen next to it.
How far are the bands in the PDL ?
64nm
What causes the bad like appearance of collagen fibres?
The highly repetitive organised assembly of tropocollagen
What is found between rows of tropocollagen?
Cross linking bonds
Why do crosslinks form in collagen?
Due to the conversion of lysine and hydroxylysine into their aldehyde forms
What does Lysyl oxidase do?
Extracellular enzyme. It converts the side chains (R groups) on some lysine and hydroxylysine residues to their aldehyde forms
What is Lysyl oxidase dependent on?
copper dependent
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.
What is the aldehyde form of the lysine side chain called?
Allysine
What is the aldehyde form of the hydroxylysine side chain called?
hydroxyallysine
Are crosslinks permanent?
No they are strong but they can be reduced in labs by strong reducing agents or during collagen turnover. but with age , non reducible cross links form in most mature connective tissues (skin-ageing), BUT the PDL is forever young and has no NO non-reducible cross links.
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
Which 2 cross linkages are the most important?
DHLN| HLN
What does turnover of the collagen mean?
When the collagen is degraded and renewed
Describe non reducible cross links
They form with age and are very stable| They cannot be broken even in a lab
What is the ratio of DHLNL:HLNL in the periodontal ligament
1.3 : 1
is higher in PDL cos in other tiss= less than 1. This is cos PDL high turnover rate.
Summarise the biosynthesis of collagen type 1
- Synthesis of individual pro alpha chains at the RER
- Hydroxylation of PRO & LYS (Require vitamin C)
- Glycosylation of HYL and ASN
- Alignment of pro α chains (disulphide bonds form)
- PROCOLLAGEN TRIPLE HELIX forms
- Golgi (more glycosylation)
- Molecule moves out of cell
- Cleavage of terminal propeptides
9.TROPOCOLLAGEN forms - Aggregation, ¾ stagger array
- Formation of intermolecular crosslinks using Lysyl oxidase
- Fibrils form
- Fibres form
List the hierarchy of type 1 collagen?
intracellular
1. Procollagen
extracellular
2. Tropocollagen
3. Microfibrils
4. Fibrils
5. Fibres
6. Fibre bundles
How is collagen broken down?
By an enzyme called collagenase
Which cells secrete collagenase?
Fibroblasts and by cells associated by inflammation and innate defence like polymorphonucleocytes
What family is collagenase part of?
Belongs to a family of enzymes known as matrix metalloproteases, or MMPs.
Describe the ideal conditions for collagenase to work at?
Neutral pH, Contain Zn++, Endopeptidase Require Ca++
What form do cells secrete collagenase as?
Cells produce collagenases as inactive precursors that are self activated after secretion
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)- prod by same cells as collagenase
What does TIMP synthesis regulate?
collagen degradation within a tissue.
What type of enzyme is collagenase?
It is an endopeptidase, cleaving collagen molecules within their length in to three quarter and one quarter length fragments.
how long are the oxytalan fibres?
10-15nm
after collagenase , what takes over to degrade the collagen fragments completely?
Gelatinises
PDL is forever young, but why is it more prone to disease?
cos its between embryonic and mature connective tissues.
