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Perio CT Biochem > Structure function & biosynthesis > Flashcards

Structure function & biosynthesis Flashcards

1
Q

What is the most abundant protein in the body? What % of the whole body protein count?

A

collagen; 25-35%

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2
Q

What are the types of collagens?

A

Fibrillar (Type 1,2,3,5,11)
Fibril-associated (Type 9,12,14,19)
Network-like (Type 4,8,10)
Beaded-filaments (Type 6)

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3
Q

How are collagen subdivided or categorized?

A

Collagen is divided based on the structures they form

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4
Q

What makes up 90% of collagen in the body?

A

Type 1,2,3,4

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5
Q

What are functional roles of collagen?

A
  • strength
  • encases and protects delicate organs
  • flexibility
  • fills sclera of eye
  • contributes to proper alignment of cells for cell proliferation and differentiation
  • influences the cell shape and size
  • mechanical forces
  • high tensile strength like in bone and dentin
  • helps damaged blood vessels initiate thrombus formation
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6
Q

The type, quantity, and quality of collagen are regulated at the level of…. (4)

A
  1. transcription (biosynthesis and processing of mRNA)
  2. translation
  3. co-transitional (intracellular)
  4. various posttranslational modifications (extracellular)
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7
Q

How does type 1 collagen exist in bone or describe the structure.

A

a hetero-trimer of two alpha-1 chains and one alpha-2 chain

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8
Q

What is the structure of type 2 and 3 collagen?

A

a homo trimer of chains encoded by a single gene

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9
Q

Explain the postranslational modification and assembly of type 1,2,3 collagen.

A

Chains consists of uninterrupted Gly-X-Y repeats.
X= proline
Y= hydroxyproline
The three chains twist into triple helices where Gly is in center and X&Y are at the surface of the triple helix. Triple helices line up and are bonded together into ropes (fibrils). Multiple fibrils are then arranged into layers to form collagen fibers.

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10
Q

What is the difference between intracellular and extracellular posttranslational modification & assembly?

A

Intracellular- formation and secretion of the triple helical procollagen molecules

Extracellular- converts the procollagen molecules into collagen and incorporates them into stable crosslinked fibrils or supramolecular structure

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11
Q

Provide the details of intracellular assembly of collagen.

A
  1. Genes for pro-alpha1 and pro-alpha2 chains are transcribed into mRNAs.
  2. mRNA is translated on the RER into prepro-alpha poly-peptide chains that are extruded into the lumen of the RER, where the signal sequence is removed.
  3. selected proline and lysine residues are hydroxylated.
  4. Selected hydroxylysine residues are glycosylated with glucose and galactose.
  5. Three pro-alpha chains assemble. Intrachain and interchain disulfide bonds form at the C-terminal propeptide extension.
  6. A triple helix is formed by zipper like folding.
  7. The procollagen molecule is secreted from a golgi vacuole into the ECM. (this is now considered extracellular once it exits golgi)
  8. The N and C terminal are cleaved by procollagen peptidase.
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12
Q

What vitamin is required for hydroxylation of proline residues?

A

Vit C

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13
Q

What is the purpose of hydroxylation?

A

stabilizes the triple helical structure of the collagen

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14
Q

What is the glycosylation process?

A

galactose and glucose are added to hydroxylysine residue.

Glycosylation if asparagine residues in propeptides

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15
Q

What is multmerization?

A

triple helix formed by inter-&intrachain disulfide bonds at the N & C terminus. Triple helix formation stops additional hydroxylation.

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16
Q

Explain postranslational modificaton and assembly extracellularly.

A
  1. Enzymatic digestion of procollagen. The N&C terminal pro-peptides are cleaved by procollagen peptidase.
  2. Free N terminal propeptides acts as feedback regulators of collagen translation.
  3. Fibrillogenesis of collagen. Triple helixes line up and are bonded together into ropes (fibrils). Multiple fibrils are then crosslinked into layers to form collagen fibers. Fibers are stabilized through covalent bonds between lysine residues present inside a collagen molecule (intr) and between different collagen molecules (inter). Growth and reorganization of collagen fibers. (in bone and dentin, mineral crystals are deposited in between layers.)
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17
Q

How are the collagen fibers oriented in tendons?

A

parallel

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18
Q

How are the collagen fibers oriented in skin?

A

3D with some fibers running parallel to surface

19
Q

How are the collagen fibers oriented in bone?

20
Q

How are the collagen fibers oriented in elastic ligaments?

21
Q

How are the collagen fibers oriented in cartilage?

A

single fibers in random directions in proteoglycan matrix

22
Q

What fibers of the periodontium withstands the intrusive forces of mastication?

A

collagen fibers (type 1)

23
Q

Why do people get osteogenesis imperfecta?

A

mutation in either or both COL1A1, COL1A2 or mutation in CRTAP, P3H1, CyPB genes

24
Q

How is mutation with COL1A1, COL1A2 or both inherited?

A

autosomal dominant

25
Q

How is mutation with CRTAP, P3H1, CyPB inherited?

A

autosomal recessive

26
Q

What are the clinical signs of Osteogenesis imperfect?

A

brittle bones, blue/grey sclera, dentinogenesis imperfecta (translucent , discolored weak teeth)

27
Q

Is there a cure for OI?

28
Q

What causes the rate of collagen biosynthesis to decrease?

A 
aging
glucocorticoids, cortisol
anti-inflammatory steroids
IL-1, IFN-gamma, TNF-alpha
PTH
29
Q

What causes the rate of collage biosynthesis to increase?

A

PDGF
TGF-B
FGF
IGF

30
Q

What percentage of collagen is in skin? Bones? Tendons? Liver?

A 
Bones = 90%
Tendons= 85%
Skin = 70%
Liver= 4%
31
Q

Explain basic explanation of collagen degradation.

A

Normal growth and development, as well as repair of tissues, requires precise regulation of collagen breakdown. The breakdown is primarily by collagenase.

32
Q

What are MMPs?

A

MMPs are mammalian collagenases and are Ca2+ and Zn2+ endopeptidases. . Degrades most ECM proteins. Typical activity in adult tissues are normally very low but can increase significantly in various pathological conditions.

33
Q

What is the minimum sequence required for collagen cleavage?

A

Gly-Lle-Ala or Gly-Leu-Ala

34
Q

Where is type 1 cleaved at?

A

at alpha-1 chain: Gly-Lle; at alpha-2 chain: Gly-Leu

35
Q

Where is type 2 cleaved at?

36
Q

Where is type 3 cleaved at?

37
Q

Once collagenase makes the initial cuts, what other enzymes aid in collagenase activity?

A

elastase, gelatinase, neutral proteinase

38
Q

What are three ways of collagen degradation?

A
  1. phagocytosis of fragments of collagen fibrils is degrades by the lysosomal enzyme system (cathepsin B &N)
  2. True collagenase: helped with elastase gelatinase or cathepsin G
  3. Bacterial collagenases. Cleave alpha chains at site preceding glycine residues.
39
Q

What agents inhibits collagen degradation?

A

chelating agents EDTA abd phenothroline

40
Q

What are the clinical presentations of collagen degradation? (2 main) Provide examples in each main category.

A

Pathology can be characterized into two groups:

  1. Excess collagen breakdown ie rheumatoid arthritis, epidermolysis bullosa, perio dx
  2. Abnormal deficiency in mechanism of collagen degradation. ie scleroderma
41
Q

Collagen degradation in rheumatoid arthritis?

A

collagenase by inflammatory and synovial fluid cells

42
Q

Collagen degradation in epidermolysis bullosa?

A

autosomal recessive mutation in COL7A1

43
Q

Collagen degradation in periodontal dx?

A

bacterial toxins and host response activate collagenase

44
Q

Collagen degradation in scleroderma?

A

tightening of skin/CT due to increase in collagen

Perio CT Biochem (6 decks)

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