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CT Flashcards

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1
Q

Extracellular matrix vs CT

A

ECM is material outside cells and epithelial/endothelial borders

CT is cells AND ECM

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2
Q

What tissues are CT?

A

Bone, cartilage, ligament, skin, teeth, tendon, basement membrane, blood vessels, adventitia, cornea, intestinal walls

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3
Q

Function of CT

A
  • stabilize physical structure of tissues

- ACTIVELY regulate cell behaviour (development, migration, proliferation, cell shape, metabolic functions)

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4
Q

Characterization of CT based on chemical composition

A
  • proteins
  • proteoglycans
  • glycoproteins
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5
Q

4 steps of elastin fiber synthesis

A
  • transcriptions (tropoelastin and microfibril components)
  • translation
  • secretion
  • fiber formation
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6
Q

ELN trascription regulation

A

ELN is gene encoding tropoelastin

Increased transcription:
IGF-1/insulin like growth factor 1 and TGF-beta/transforming growth factor beta

Decreased transcription:
TNF-alpha, bFGF (basic fibroblast growth factor), HB-EGF (heparin binding epidermal growth like factor)

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7
Q

Tropoelastin

A
  • encoded by ELN
  • monomer, covalently crosslinked into elastin (making very insoluble)
  • secreted by ECM where it associates with microfibrils (fibrillins, MAGPs, fibulins, EMILIN-1)
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8
Q

Cross linking of tropoelastin

A
  • lysyl residues covalently crosslinked by lysyl oxidase

- makes elastin very insoluble

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9
Q

Elastin fiber physical properties

A

expands and contracts (stretches). amorphous

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10
Q

Treatment of CT with NaOH and high temperature

A
  • solubilizes virtually all proteins

- since elastin is so insoluble, what’s left after treatment is pure elastin

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11
Q

elastase

A

cleave insoluble elastin

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12
Q

elastin related disorders (6)

A
  • cutis laxa
  • supravalvular aortic stenosis
  • William’s syndrome
  • COPD
  • Atherosclerosis
  • Aortic aneurysm
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13
Q

Role of ELN gene in tooth movement

A
  • After external pressure, mRNA levels of ELN increased significantly
  • ELN gene could then be important in orthodontic tooth movement
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14
Q

Marfan’s syndrome

A

-mutation of fibrillin (microfibril related disorder)

Fibrilin mutation –> TGF beta –> matrix metalloproteases –> tissue degredation –>

  • Cardiovascular, ocular, skeletal (bone overgrowth and joint laxity) problems
  • periodontal disease
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15
Q

Proteoglycans

definition, location, physical properties

A
  • form highly hydrated, gel like ground substance
  • direct and indirect (via other substances being imbedded in proteoglycans) function
  • intracellular, membrane associated or extracellular
  • carbohydrate rich with some proteins
  • bind water and cations
  • polyanions
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16
Q

Proteoglycans function

A

determine visoelastic properties of joints, withstand compression, permeable, lipid metabolism, hemostasis and thrombosis, matrix assembly and cell adhesion, migration, proliferation, and differentiation.

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17
Q

proteoglycan associated disorders (4)

A
  • osteoporosis
  • osteoarthritis
  • Ehler’s Danlos syndrome (progeroid varient, skin fragility)
  • corneal diseases
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18
Q

Proteoglycans in the oral cavity

A
  • postulated roles in tooth development, dentin formation/mineralization, adhesion and fusion of palatal shelves,
  • roles remodeling of oral tissues –> involved in periodontal regeneration (decorin up-regulated and biglycan down-regulated)
  • perlecan (heparin sulfate) may stimulate bone regeneration bu also may play role in tumorigenesis
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19
Q

Proteoglycan structure

A
  • core protein
  • covalently linked GAG
  • proteins and GAG = proteoglycans
  • different core proteins, GAG types and number of chains, and chain length of GAG makes differences in PG
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20
Q

GAG basic structure

A
  • disaccharide repeating unit (long or short)
  • have either glucosamine or galactosamine (amino sugar derivatives)
  • one neg charged sugar
  • neg charged groups either COOH or sulfate groups
  • hydration and charge vary
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21
Q

Hyaluronic acid

A

heteropolymer of alternating glucuronic acid and N-acetylglucosamine

the only GAG that is not covalently linked to protein core (Free)

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22
Q

Major GAGs (6)

A

chondroitin 6-sulfate, keratin sulfate, chondroitin 4 sulfate, heparin sulfate, heparin, dermatan sulfate

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23
Q

Aggrecan aggregate

A
  • large(!!!), complex, proteoglycan

- aggrecan monomers associate with hylauronic acid to make aggrecan aggregate

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24
Q

Glycoprotein subfamilies (3)

A

Fibronectins (widely distributed)
Laminins (basal laminae)
Collagens (most widely distributed protein in body)

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25
Glycoprotein-carbohydrate
-glycoproteins covalently bound to carbohydrate: - the amide NH2 group of asparagine: N linked - hydroxyl OH group of serine or theonine: O linked - hydroxyl OH group of hydroxylysine (only in collagens): O linked
26
Role of sugars in glycoprotein
- make more hydrophilic - help protein folding/tertiary structure - stabilize against hydrolysis and modulate biding of some components
27
Linker proteins
Some glycoproteins are linker proteins - Fibronectin - laminin - chondronectin: in cartilage; links chrondocytes, type II collagen, cartilage proteoglycans - thrombospondin: in blood plasma/ECM; links fibronectin, laminin, type V collagen, cell surface receptors, fibrinogen - vitronectin: bone - entactin: basal laminae - nidogen: basal laminae
28
Fibronectin | location/function
- in ECM/blood plasma - links types I, III, IV collagen, cell surface receptors, heparin, heparin sulfate, hyaluronic acid - enable cells to interact with ECM - determine cell morphology, embryonic cell migration, adhesion, differentiation, wound healing, structural support
29
Fibronectin/cancer
many cancer cells lose ability to synthesize fibronectin: may lead to migration of cancer cells in metastatic cancers
30
Fibronectin in oral cavity
-dental mesenchyme differentiating into odontoblasts regulated by fibronectin
31
Fibronectin structure
- family of glycoproteins - 5% carbohydrate by weight - 2 chains linked by disulfide bond near C terminal making V structure - RGD or RGDS sequence in cell surface receptor binding domain (for binding cell surface receptors and ECM)
32
Laminin | location/function
- in basal laminae - links type IV collagen (high affinity), fibrin, heparin sulfate GAGs, other laminin molecules - enable epithelial cells to interact with ECM - maintain polarized differentiated phenotype of epithelial cells, embryonic nerve axonal outgrowth, nerve regeneration, adhesion, motility
33
Laminin in oral cavity
- laminin-332 (laminin 5) contributes to growth and terminal differentiation of ameloblasts, and enamel matrix formation - expression of alpha2 and beta2 chain in fetal oral squamous epithelium and in adult oral squamous cell carcinomas
34
laminin structure
- family of glycoproteins - 13%carbohydrate by weight - special domains bind cell surface receptors to ECM - 3 polypeptide chains (alpha, beta, gamma); disulfide linked heterotrimer - polypeptides in cruciform (cross) shape - self associate to form aggregates
35
laminin nomenclature
- indicates chain composition of alpha, beta, gamma chain | ie. laminin 332 is (alpha3, beta3, gamma2)
36
Integrins function
- transmembrane glycoproteins - cytoplasmic side binds to cytoskeletal components - extracellular side binds to fibronectins and laminins (forms basis for linker protein-mediated communication) - activation via outside in or inside out signalling
37
integrin structure
- transmembrane glycoproteins - 2 polypeptides (alpha and beta) - RGD/RGDS sequence on linker proteins binds specificially to integrin receptors - activation of integrins can lead to clustering and formation of focal adhesions
38
Collagen basics
- structural role (stress bearing), cell attachment, differentiation, chemotaxis - 1/4 of proteins in vertebrates in collagen by weight - 28-30 types
39
Steps in collagen fiber formation (7)
- transcription - translation - post translational modification - secretion as procollagen - processing to tropocollagen (not all, type IV doesn't) - associate with ECM - insolubilization into ECM
40
Collagen nomenclature
- 3 polypeptides: either homotrimers (Types II and III) or heterotrimers (Types I, IV, V) - each polypeptide is alpha chain - 1 for homotrimers; 1 and 2 or 1,2,3 for heterotrimers - roman numerals for collagen type designation ie. Type I collagen: alpha1(I), alpha1(I), alpha2(I) Type II collagen: alpha1(II), alpha1(II), alpha1(II)
41
Collagen structure
- tertiary: left handed type II trans helix - quaternary: right handed superhelix - fibrous proteins - form insoluble fibers with high tensile strength - aa composition: 1/3 glycine; charged/positive aa (proline, Hyp/hydroxyproline, hydroxylysine); polar, basic aa also found - largely repeats of gly-X-Y (often x=pro, y=hyp)--->regular repeating structure
42
Collagen gene transcription control
TGF-beta signal from outside cell to stimulate gene transcription via SMAD IL-1beta signal from outside cell to stimulate gene transcription TNF-alpha signals from outside cell to inhibit gene transcription Several transcription factors interact with enhancer/repressor elements in promoter region
43
collagen gene transcription nomenclature
Eg | COL1A1, COL1A2, COL3A1
44
Collagen translation
-synthesized on membrane bound ribosomes as larger precursor
45
collagen post translational modifications
- occur cotranslationally | - include hydroxylation of prolyl and lysyl residues, and glycosylation of hydroxylysyl residues
46
prolyl hydroxylase
- hydroxylates prolyl residues in collagen - has Fe++ ion at active site - dioxygenase - requires ascorbate - proline hydroxylated at C4 only if pro is on amino side of gly (different enzyme if on carboxyl side)
47
Scurvy
- dietary deficiency of vitamin C (ascorbate) | - poor calcification of developing teeth (inhibition of collagen formation of dentin & cementum)
48
lysyl hydroxylase
- hydroxylates lysyl residues - free lysine not a substrate - hydroxlation of lysine only if on amino side of glysine - requires ascorbate
49
Ehler's-Danlos Type VI
- lysyl hydroxylase dificiency | - lowered crosslinking of collagens
50
Collagen glycosylation
- n linked or O linked - unique to collagens: glycosylated hydroxylysyl residues - glucose/galactose disaccharide - degree of glycosylation varies with tissue type
51
procollagen
-after post translational modification two alpha1(I) and one alpha2(I) procollagen associate to form triple helical procollagen -formed in lumen of ER, packaged and secreted by passing through Golgi -h bonding between N-H of Gly and O of suceeding reside of other chain in 3 polypeptide chains -vertically staggered so gly-x-y on same level along helix axis STRONG
52
Collagen stability
depends on: - h bonds between N-H of Gly and C=O of second residue in triplet on other chain - gly as 3rd aa (makes close packing of aa) - Hyp content (more is more stable, -OH groups also participate in H bonding) - total imino acid content (more is more stable) Animals with higher body temperature need higher Tm so more stability.
53
Tm for measuring collagen stability
measure temperature vs viscosity | Tm is temperature when 1/2 helical structure is lost
54
OI (osteogenesis imperfecta)
- mutation of single glycine to cysteine at residue 988 - triple helix disrupted - skeletal deformities, brittle bones
55
Ehler's-Danlos Type IV
- defects in type III collagen (gly, skip exon) - thin, translucent skin - bruise easily - rupture arteries - perforate intestines - rupture uterus
56
Collagen modification in ECM
- procollagen peptidases cleave N and C terminal of Types I, II, II (not IV) --> product called tropocollagen - N terminal propeptides have intrachain disulfides, C terminal propeptides have interchain disulfides - tropocollogen contains entire Gly-x-y repeat region and telopeptides
57
Ehler's-Danlos Type VII
- from deficiency in procollagen peptidases - hyperextensible skin that bruises easily - dislocation of major joints
58
Collagen fibril assembly
Types I, II, III tropocollagen molecules align with 1/4 stagger with 400A gaps between head and tail (site of cross link formation and nucleation site for calcium deposition in bone; also dark part in stains) adjacent rows have 680A gap between them
59
Cross linking collagen into fiber
- oxidation of lysyl and hydroxylysyl (only in collagen) catalyzed by lysyl oxydases - spontaneous condensations of products from above form covalent bonds between adjacent tropocollagen molecules
60
lysyl oxidase
- ε amino termini of lysyl residues converted to aldehydes in the presence of O2 - requires Cu++
61
Hydroxypyridinium
AKA pyridinoline - cross link unique to collagen - formed by cross link of two hydroxylysyl residues and a lysyl residue in collagen
62
Desmosine
cross link unique to elastin - 3 lysines converted to allysines via lysine amino oxidase - aldol condensations form desmosine (or isodesmosine) cross link
63
Collagenases
- cleave collagen - in family MMP (matrix metalloproteinases) - cleave in the triple helical region of collagens - critical to tissue remodeling in vertebrates - in vertebrates cleave ~1/4 from C terminus

Biochem 3 (5 decks)

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