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Histology/Cell Biology > Extracellular Matrix > Flashcards

Extracellular Matrix Flashcards

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1
Q

Why is the basement membrane considered an ECM?

A
  • exterior to cells
  • made by both epithelial and connective tissue
  • main functions are communicating with cells and binding them to underlying connective tissue
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2
Q

Describe some of the characteristics of ECM

A
  • generally, medium is gel-like
  • complex and intricate structural network that surrounds and supports cells within the connective tissue
  • composed fibers (collagen/elastic), proteoglycans, proteins like laminin/fibronectin, GAG’s
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3
Q

What allows for integrin and laminin to bind?

A
  • this binding mediates the binding of the rest of the matrix
  • integrins composed of alpha and beta structure
  • dimer has binding site for amino acid motif RGD on outer membrane surface and binds to cytoskeleton on inner membrane surface
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4
Q

Describe some characteristics of the interstitial matrix

A
  • has cells scattered throughout
  • cells are not connected to each other
  • contains fibroblasts that have integrins, which bind with fibronectin, which in turn binds to proteoglycans and collagen
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5
Q

fibronectin

A
  • two chains linked via disulfide bridge
  • contains several binding domains that interact with dif ECM molecules and integrin
  • important in cell attachment to ECM
  • in tissues, it forms fibers and aggregates
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6
Q

fibrillar collagen

A

type I collagen

formed from braids of chains

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7
Q

laminin

A

formed from three different protein chains

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8
Q

tenascin

A

formed from six different protein chains

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9
Q

type IV collagen

A
  • long protein chain in kinks

- does not form fibers

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10
Q

hyaluronan

A
  • very long polysaccharide
  • contains amino sugars (very unusual)
  • also called glycosaminoglycan (GAG)
  • no protein attached
  • found outside animal tissue)
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11
Q

decorin

A
  • GAG chain and protein covalently attached
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12
Q

perlecan

A
  • present in cartilage almost exclusively
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13
Q

aggrecan

A
  • core protein of proteoglycan

- many chains attached

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14
Q

Describe the EM of dense type I collagen ECM

A
  • bundles of fibrils with striped pattern –> most prominent in type I collagen
  • quasi-crystalline structure
  • stain binds to different parts of the fiber in a regular fashion creating stripes
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15
Q

Describe the assembly of type I collagen

A
  1. triple helices (tropocollagen aska collagen molecules)
    - consists of two identical chains (both specified by same gene) and one dif chain (dif gene)
  2. collagen molecules assemble into fibrils
  3. fibrils assemble into fibers
  4. depending on tissue type, fibers assemble into mesh (sometimes need strength in all directions) or in one direction (i.e. tendon)
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16
Q

Describe EM of type I collagen fibers of cornea of eye

A
  • fibrils lined up in sheet (viewed longitudinally)
  • next layer has fibrils in cross section
  • collagenous, densely packed tissue but still able to have light pass through it due to crystalline (para-crystalline) organization
17
Q

What is the importance of reticular connective tissue in the production of collagen?

A
  • found in the lymph nodes and spleen
  • makes type III collagen
  • much finer fibrils that don’t assemble into fibers
  • secreted by cell but don’t detach from cell (remain embedded)
  • cells and fibers both make up a reticulum (network)
  • creates storm for lymphocytes
18
Q

Name the most abundant protein in the animal kingdom

A
  • type I collagen
  • found almost everywhere in body (skin, tendon, bone, etc.)
  • makes up about 40% of proteins in the body
19
Q

What are the minor collagens?

A
  • types V-XII

- not very abundant but very significant when talking about collagen disorders

20
Q

Describe the cause of Classic Ehlers-Danlos syndrome (types I and II) and describe the symptoms

A
  • due to mutations in COL5A1 and COL5A2 (mutation in type V collagen)
  • causes hyper extension of joints and weakness of skin
21
Q

collagen disorders

A
  • some caused by mutations
  • when collagen assembles, covalent cross linked from prolines or lysine become hydroxylated by enzymes
  • impaired hydroxylating enzymes forms weak collagen
  • hydroxylating enzyme may require cofactor (vitamin C), without which proline will not be hydroxylated
  • collagen made with pro-peptides that are removed, but impaired enzyme may not remove pro-peptide
22
Q

Describe EM of elastic connective tissue

A
  • elastin can form sheets and fibers
  • gives connective tissue a rubbery consistency
  • found in organs that need to expand and snap back rapidly (i.e. aorta and other large blood vessels, Pina of ear, airways of lungs)
  • tissues that make elastin also make fibrillin
23
Q

Describe mechanism of elastin

A
  • unusual polypeptide backbone of elastin causes random coiling in normal, relaxed state
  • stretching causes elastin molecules to straighten out, but still held to one another via cross-link
  • removal of stretching force allows elastin molecules to coil again
24
Q

importance of fibrillin

A
  • acts as a scaffold for elastin

- mutations in fibrillin gene lead to disruptions in elastin

25
Q

Marfan syndrome

A
  • caused by mutations in fibrillin gene
  • absence of elastin-associated fibrillin mircrofibrils –> abnormal elastic tissue
  • fibrillin acts as a repository for storage forms of growth factors
  • microfibrils bind directly to cell through integrins
  • in fibrillinopathies, integrin not binding microfibril, and growth factor goes unregulated
  • causes compromise of mechanical interaction
26
Q

fibronectin

A
  • can bind to ECM or cell surface
  • amino acid motif RGD to cell-binding domain
  • heparan binding domain (ECM)
  • collagen binding –> type I collagen
  • regulatory factor for development and wound repair
27
Q

proteoglycans

A
  • consist of protein core and one or more covalently attached (O-linked) glycosaminoglycan (GAG) chains
  • many straight chains of very long sugars with repeating monomers
  • linked to membrane or embedded as integral membrane protein
  • most are free in the ECM but various diseases result when proteoglycans prevented from binding to PM
28
Q

glycoproteins

A
  • proteins with carbohydrates attached (N-linked and O-linked)
  • sugar chains are branched
    i. e. fibronectin and laminin
29
Q

common GAG’s

A
  • hyaluronan
  • heparan sulfate
  • chondroitin sulfate
  • dermatan sulfate
30
Q

Describe how cell-cell adhesions play a role in cancers and tumor invasion

A
  • cells bind via non-junctional adhesions

- cell binding is more transit and more temporary

31
Q

What are the different junctional adhesion counterparts?

A
  • focal contact (integrin binding to actin cytoskeleton) and adhesion belt (actin)
  • hemi-desmosome (integral binding to intermediate filament) and desmosome (intermediate filament)
32
Q

Describe function of basal lamina in kidney function

A
  • epithelial tissue on either side with thick basal lamina between them
  • found in filtration region of kidney
  • involved in filtration
33
Q

What composes the reticular lamina?

A
  • reticular fibers (type III collagen)
  • anchoring fibrils (type VII collagen)
  • anchoring plaques (type IV collagen)
  • very elaborate connections that create great structural integrity
34
Q

role of adaptor proteins in integrin binding

A
  • adaptor proteins bind to actin or intermediate filaments in cytoplasm of cell when extracellular matrix protein binds to integrin subunits in extracellular space
  • nucleus can produce adaptor proteins that link to integrins on inside that help organized ECM
  • matrix proteins can be dissolved, allowing cell to become motile
35
Q

transmembrane co-localization of fibronectin fibers and actin filaments

A
  • fibronectin fibers found on cell surface
  • actin filaments found within cell
  • by tracing fibers, see that there is tight coordination between extracellular and intracellular appendages

Histology/Cell Biology (12 decks)

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