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Biochem 3 > CT > Flashcards

CT Flashcards

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
Q

Glycoprotein-carbohydrate

A

-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
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26
Q

Role of sugars in glycoprotein

A
  • make more hydrophilic
  • help protein folding/tertiary structure
  • stabilize against hydrolysis and modulate biding of some components
27
Q

Linker proteins

A

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
Q

Fibronectin

location/function

A
  • 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
Q

Fibronectin/cancer

A

many cancer cells lose ability to synthesize fibronectin: may lead to migration of cancer cells in metastatic cancers

30
Q

Fibronectin in oral cavity

A

-dental mesenchyme differentiating into odontoblasts regulated by fibronectin

31
Q

Fibronectin structure

A
  • 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
Q

Laminin

location/function

A
  • 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
Q

Laminin in oral cavity

A
  • 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
Q

laminin structure

A
  • 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
Q

laminin nomenclature

A
  • indicates chain composition of alpha, beta, gamma chain

ie. laminin 332 is (alpha3, beta3, gamma2)

36
Q

Integrins function

A
  • 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
Q

integrin structure

A
  • 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
Q

Collagen basics

A
  • structural role (stress bearing), cell attachment, differentiation, chemotaxis
  • 1/4 of proteins in vertebrates in collagen by weight
  • 28-30 types
39
Q

Steps in collagen fiber formation (7)

A
  • transcription
  • translation
  • post translational modification
  • secretion as procollagen
  • processing to tropocollagen (not all, type IV doesn’t)
  • associate with ECM
  • insolubilization into ECM
40
Q

Collagen nomenclature

A
  • 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
Q

Collagen structure

A
  • 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
Q

Collagen gene transcription control

A

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
Q

collagen gene transcription nomenclature

A

Eg

COL1A1, COL1A2, COL3A1

44
Q

Collagen translation

A

-synthesized on membrane bound ribosomes as larger precursor

45
Q

collagen post translational modifications

A
  • occur cotranslationally

- include hydroxylation of prolyl and lysyl residues, and glycosylation of hydroxylysyl residues

46
Q

prolyl hydroxylase

A
  • 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
Q

Scurvy

A
  • dietary deficiency of vitamin C (ascorbate)

- poor calcification of developing teeth (inhibition of collagen formation of dentin & cementum)

48
Q

lysyl hydroxylase

A
  • hydroxylates lysyl residues
  • free lysine not a substrate
  • hydroxlation of lysine only if on amino side of glysine
  • requires ascorbate
49
Q

Ehler’s-Danlos Type VI

A
  • lysyl hydroxylase dificiency

- lowered crosslinking of collagens

50
Q

Collagen glycosylation

A
  • n linked or O linked
  • unique to collagens: glycosylated hydroxylysyl residues
  • glucose/galactose disaccharide
  • degree of glycosylation varies with tissue type
51
Q

procollagen

A

-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
Q

Collagen stability

A

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
Q

Tm for measuring collagen stability

A

measure temperature vs viscosity

Tm is temperature when 1/2 helical structure is lost

54
Q

OI (osteogenesis imperfecta)

A
  • mutation of single glycine to cysteine at residue 988
  • triple helix disrupted
  • skeletal deformities, brittle bones
55
Q

Ehler’s-Danlos Type IV

A
  • defects in type III collagen (gly, skip exon)
  • thin, translucent skin
  • bruise easily
  • rupture arteries
  • perforate intestines
  • rupture uterus
56
Q

Collagen modification in ECM

A
  • 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
Q

Ehler’s-Danlos Type VII

A
  • from deficiency in procollagen peptidases
  • hyperextensible skin that bruises easily
  • dislocation of major joints
58
Q

Collagen fibril assembly

A

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
Q

Cross linking collagen into fiber

A
  • 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
Q

lysyl oxidase

A
  • ε amino termini of lysyl residues converted to aldehydes in the presence of O2
  • requires Cu++
61
Q

Hydroxypyridinium

A

AKA pyridinoline

  • cross link unique to collagen
  • formed by cross link of two hydroxylysyl residues and a lysyl residue in collagen
62
Q

Desmosine

A

cross link unique to elastin

  • 3 lysines converted to allysines via lysine amino oxidase
  • aldol condensations form desmosine (or isodesmosine) cross link
63
Q

Collagenases

A
  • 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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