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ODDR- biochemistry > biochem1 > Flashcards

biochem1 Flashcards

1
Q

What is the origin of all connective tissues?

A

Mesodermal origin

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2
Q

Give an example of a connective tissue in the periodontium?

A

The periodontal ligament

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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

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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

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5
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.

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6
Q

Give an example of the major fibres found in the ECM

A

Collagen

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7
Q

Give an example of the minor fibres found in the ECM

A

Oxytalan| Elastin

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8
Q

What makes up 3% of the ECM?

A

The minor fibres

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9
Q

What do elastic fibres do in connective tissues?

A

They provide elasticity to the tissue

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10
Q

What are mature elastic fibres made up of?

A

2 components:
1. Microfibrillar component (10%)
2. Inner core (or the filling) 90%

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11
Q

Describe the microfibrillar component of mature elastic fibres

A

It is an external tube like structure in the elastic fibre

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12
Q

Describe the Inner core component of mature elastic fibres

A

It is the “filling”, made up of an amorphous polymeric protein called elastin

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13
Q

How much of the mature elastic fibre is made up of elastin protein?

A

90%

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14
Q

Name the minor fibres in the PDL in increasing level of maturity

A

Oxytalan > Elaunin > Elastin

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15
Q

What do most mature connective tissues have in their ECM?

A

Elastin fibres

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16
Q

What are elastin fibres made up of?

A

Microfibrillar protein plus its elastin core

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17
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.

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18
Q

What are the microfibrillar fibres at the foetal stage called?

A

Oxytalan fibres

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19
Q

What are immature elastin fibres called?

A

Oxytalan fibres

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20
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”.

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21
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

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22
Q

What is the major fibrous component of connective tissues?

A

COLLAGEN

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23
Q

What do collagen fibres look like under the microscope?

A

Collagen fibrils have a characteristic striped or banded appearance.

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24
Q

What is the periodontium?

A

tissues that attaches to the tooth to the jaw

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25
Q

What are 4 components of the periodontium?

A

AV bone, cementum (calcified)
PDL, lamina propria of gingiva (non-calcified)

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26
Q

What are all types of connective tissues made up of?

A
  1. Cells| 2. A grond substance or extracellular matrix
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27
Q

What is the ground substance?

A

Ground substance is a jelly like substance that contains fibres, cells vascular tissue and nerves

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28
Q

When does the ground substance become extracellular matrix?

A

When the jelly like pool combines with fibres that form the tissue

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29
Q

What do fibroblasts do?

A

Form all the collagen fibres and secretes enzyme that degrades them

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30
Q

Describe the protein core of young elastin fibres

A

The protein core is smaller in younger fibres

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31
Q

Describe oxytalan

A

They are immature minor fibres. They are only made up of the microfibrillar coat it is hollow without a protein core

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32
Q

What happens to oxytalan as the tissue matures?

A

Protein begins to deposit inside the microfibrilar coat until the core is no longer hollow

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33
Q

What is matured oxytalan called?

A

elaunin

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34
Q

What is mature elaunin called?

A

Elastin

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35
Q

Which minor fibres make up the PDL?

A

Oxytalan and elaunin

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36
Q

Which minor fibre is NOT found in the PDL?

A

Elastin

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37
Q

The fact that the PDL doesn’t contain any mature elastin shows what?

A

It maintains some embryonic characters

38
Q

Which type of collagen is most abundant in the body?

A

Type 1 collagen

39
Q

What are all types of collagen made up of?

A

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.

40
Q

Which type of collagen predominantly makes up the PDL?

A

Type 1 (80% of all collagen fibres in the PDL are type 1)

41
Q

Name the types of collagen that made up the PDL

A

Type 1 (80%)Type 3 (20%)

42
Q

Name the percentage of type 3 collagen found in mature, embryonic and PDL connective tissues

A

Mature: 10% Embryonic: 30% PDL: 20%
hence, PDL is more immature rather than mature (it does not mature over time)

43
Q

Name the structure of collagen type 1

A

Triple helical structure (braid like structure)

44
Q

What is the structure of the polypeptide chains

A

repeating tri-peptide structure of glycine (GLY) followed by proline/hydroxyproline and then alanine
[-GLY-PRO-ALA] or [-GLY-HYP-ALA-]

45
Q

What would we see if we were to look down at a cross section of a single type 1 collagen molecule?

A

We would see that the glycine is facing the middle while the other 2 amino acids are facing outwards

46
Q

Why does glycine appear to be facing the middle when we look at a cross section of a single type 1 collagen molecule?

A

As glycine is has a small side chain which can easily fit without steric hindrance

47
Q

What is th importance of glycine facing the middle in a cross section of a single type 1 collagen molecule?

A

Glycine forms hydrogen bonds between the 3 poly peptide chains making sure the triple helical structure of collagen is stable

48
Q

What would the consequence be of a mutated glycine molecule in collagen?

A

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

49
Q

What is osteogenesis imperfecta?

A

The brittle bone disease| Due to a mutation in glycine resulting in unstable collagen type 1

50
Q

Where is type I collagen found?

A

Bone, dentine, skin, tendon, ubiquitous except in cartilage

51
Q

Where is type III collagen found?

A

It is Co-expressed with Type I, varies with age in different tissues. Foetal skin, blood vessels

52
Q

How does proline turn into hydroxyproline?

A

By the proline hydroxylase enzyme

53
Q

What proline hydroxylase enzyme need to work?

A

Vitamin C

54
Q

What disease can occur due to lack of vitamin C?

A

Scurvy (vascular fragility)

55
Q

Which cell is reasonable for collagen secretion?

A

Fibroblasts

56
Q

procollagen vs tropocollagen?

A

pro= pre-cursor of collagen, inside the cell. cut off the globular proteins (pro peptides) and u get..
tropo= outside the cell

57
Q

Describe the process of collagen formation

A
  1. Individual separated alpha chains for type I collagen are produced at the ribosomes in the RER
  2. 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)
  3. the chains link together w disulphide bonds, which regulate the collagen to start braiding the triple helicase structure.
  4. when done, another globular protein (pro peptide), hair tie is added at the bottom to hold THS together.
  5. procollagen is secreted outside, into extracellular matrix, and pro peptides are cut off, leaving tropocollagen to join w other tropos and form collagen fibrils.
58
Q

What is the importance of pro peptides (hair ties)

A

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

59
Q

What stabilises the tropocollagen molecule?

A

disulphide bonds that form across the three chains at the carboxyl terminals

60
Q

How do procollagen fibres become able to form fibres?

A

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.

61
Q

What are pro collagen molecules without the Pro-peptides called?

A

Tropocollagen

62
Q

What would happen if the enzyme propeptidases is missing?

A

Collagen type 1 will not form fibres and so there wont be strong crosslinked structres in the bodyLethal

63
Q

How does the stagger aggregation of tropocollagen occur?

A

in a highly ordered fashion
one individual tropcollagen moves by 3/4 of its length from the tropcollagen next to it.

64
Q

How far are the bands in the PDL ?

A

64nm

65
Q

What causes the bad like appearance of collagen fibres?

A

The highly repetitive organised assembly of tropocollagen

66
Q

What is found between rows of tropocollagen?

A

Cross linking bonds

67
Q

Why do crosslinks form in collagen?

A

Due to the conversion of lysine and hydroxylysine into their aldehyde forms

68
Q

What does Lysyl oxidase do?

A

Extracellular enzyme. It converts the side chains (R groups) on some lysine and hydroxylysine residues to their aldehyde forms

69
Q

What is Lysyl oxidase dependent on?

A

copper dependent

70
Q

What makes lysyl oxidase unusual?

A

It is unusual in its ability to be able to be active on proteins that are present within fibrillar structures rather than being free.

71
Q

What is the aldehyde form of the lysine side chain called?

A

Allysine

72
Q

What is the aldehyde form of the hydroxylysine side chain called?

A

hydroxyallysine

73
Q

Are crosslinks permanent?

A

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.

74
Q

What happens once the aldehyde form of lysine and hydroxylysine have formed?

A

They will go on to form stable covalent cross links between collagen molecules within the fibrils

75
Q

Which 2 cross linkages are the most important?

A

DHLN| HLN

76
Q

What does turnover of the collagen mean?

A

When the collagen is degraded and renewed

77
Q

Describe non reducible cross links

A

They form with age and are very stable| They cannot be broken even in a lab

78
Q

What is the ratio of DHLNL:HLNL in the periodontal ligament

A

1.3 : 1
is higher in PDL cos in other tiss= less than 1. This is cos PDL high turnover rate.

79
Q

Summarise the biosynthesis of collagen type 1

A
  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
  9. Aggregation, ¾ stagger array
  10. Formation of intermolecular crosslinks using Lysyl oxidase
  11. Fibrils form
  12. Fibres form
80
Q

List the hierarchy of type 1 collagen?

A

intracellular
1. Procollagen

extracellular
2. Tropocollagen
3. Microfibrils
4. Fibrils
5. Fibres
6. Fibre bundles

81
Q

How is collagen broken down?

A

By an enzyme called collagenase

82
Q

Which cells secrete collagenase?

A

Fibroblasts and by cells associated by inflammation and innate defence like polymorphonucleocytes

83
Q

What family is collagenase part of?

A

Belongs to a family of enzymes known as matrix metalloproteases, or MMPs.

84
Q

Describe the ideal conditions for collagenase to work at?

A

Neutral pH, Contain Zn++, Endopeptidase Require Ca++

85
Q

What form do cells secrete collagenase as?

A

Cells produce collagenases as inactive precursors that are self activated after secretion

86
Q

How are collagenases turned off after being active?

A

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

87
Q

What does TIMP synthesis regulate?

A

collagen degradation within a tissue.

88
Q

What type of enzyme is collagenase?

A

It is an endopeptidase, cleaving collagen molecules within their length in to three quarter and one quarter length fragments.

89
Q

how long are the oxytalan fibres?

A

10-15nm

90
Q

after collagenase , what takes over to degrade the collagen fragments completely?

A

Gelatinises

91
Q

PDL is forever young, but why is it more prone to disease?

A

cos its between embryonic and mature connective tissues.

ODDR- biochemistry (3 decks)

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