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BMSC 220 > Topic 12: Extracellular Matrix and Cell-Cell Interactions > Flashcards

Topic 12: Extracellular Matrix and Cell-Cell Interactions Flashcards

1
Q

Extracellular Matrix (ECM)

A
  • where most animal cells in tissues are embedded
  • fills space between cells and binds cells and tissues together
  • amount of ECM varies within tissue type
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2
Q

Epithelial Tissues

A
  • basal lamina underlies epithelial cells, and binds them to underlying connective tissues
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3
Q

Muscle, Adipose, Nerve Tissues

A
  • surrounded by a thin basal lamina
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4
Q

Connective Tissue

A
  • bone, tendon, cartilage, loose connective tissue underlying skin
  • composed predominantly of ECM
  • -> component principally responsible for form and function of tissue
  • cells play a generative and supportive role for the ECM in these tissue types
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5
Q

Basal Lamina

A
  • sheetlike ECM
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6
Q

Organization of ECM

A
  • composed of tough fibrous structural proteins embedded in a gel-like polysaccharide material (GROUND SUBSTANCE)
  • -> diff. tissues vary in amount and organization of above components
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7
Q

Specialized Adhesion Proteins

A
  • anchor cells to ECM
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8
Q

Collagen

A
  • the major structural protein of the ECM
  • single most abundant protein in animal tissues
  • large family of proteins containing at least 27 diff. members
  • -> form straight fibrils and fibres and networks
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9
Q

Collagen Classes

A
  1. Fibril-forming (type I)
  2. Network-forming (type IV)
  3. Fibril-associated
  4. Anchoring
  5. Transmembrane
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10
Q

Basic Structure of Collagen

A
  • amino acid primary sequence = triple repeat of Gly-X-Y
  • X: proline; Y: hydroxyproline
  • -> stabilizes collage triple helicies
  • hydroxylysine also present
  • 3 polypeptide chains wound around each other**
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11
Q

Collagen Fibrils

A
  • formed when collagen triple helices line up in staggered arrangement and are cross-linked together
  • assembly takes place in ECM following secretion of procollagen from cell via ER/Golgi pathway
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12
Q

Procollagen

A
  • partially processed precursor of collagen
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13
Q

Collagen Fibres

A
  • bundles of collagen fibrils

- collagen is secreted as subunits of procollagen that then is assemble into fibril and fibres outside of cell

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14
Q

Elastic Fibres

A
  • found in connective tissues
  • are particularly abundant in organs that regularly stretch and then return to their original shape
  • ex) lungs
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15
Q

Elastin

A
  • principal protein of elastic fibres

- cross-linked into a network by covalent bonds formed between the side chains of lysine residues

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16
Q

Glycosaminoglycans (GAGs)

A
  • gel-forming (frequently sulphated) polysaccharides of ECM that consist of repeating units of disaccharides
  • neg. charge binds pos. charged ions, attracting and trapping water molecules, creating hydrated gel-like structure
  • GAGs covalently linked to specific proteins to form hight order structures known as proteoglycans
17
Q

Proteoglycans

A
  • large, branching glycoproteins containing up to 95% carbohydrate by weight
  • ex) aggrecan (chondroitin sulfate is the GAG attached to a core protein
18
Q

Higher Order Organization of Matrix Polysaccharides

A

i) GAGs
ii) Proteoglycans
iii) Larger proteoglycan aggregates

19
Q

Larger Proteoglycan

Aggregates

A
  • A number of proteoglycans interact with hyaluronan chains (GAGS) to form large complexes in the extracellular matrix
20
Q

Matrix Adhesion Proteins

A
  • the final class of ECM constituents
  • responsible for linking the components of the matrix to one another and the the surfaces of cells
  • Fibronectin and Laminin
21
Q

Fibronectin

A
  • dimeric glycoprotein
  • the principal adhesion protein of connective tissues
  • consists of proteoglycan, integral, collagen binding sites
22
Q

Laminin

A
  • the principal adhesion protein of the basal lamina
  • a heterotrimer with 3 subunits
  • consists of Nidogen and Agrin
23
Q

Nidogen

A
  • protein that links laminin to collagen type IV
24
Q

Agrin

A
  • large proteoglycan of ECM
25
Q

Integrins

A
  • major cell surface proteins responsible for the attachment of cells to the ECM
  • can bind to peptide sequences in collagen, fibronectin, laminin
  • serve as anchors for the cytoskeleton within the cell
  • provides linkage between cytoskeleton intracellularly and ECM
  • serve as receptors that activates intracellular signalling pathways in response to signals within ECM
  • -> control cell movement, proliferation
26
Q

Structure of Integrins

A
  • consist of dimers of 1 alpha and 1 beta subunit

- outer receptor (matrix binding) and inner (cytoskeleton binding) regions

27
Q

Types of Cell-Matrix Interactions

A
  1. Focal Adhesions
  2. Hemidesmosomes
    - both form localized sites of adhesion between the cell and ECM
28
Q

Focal Adhesions

A
  • a type of cell-matrix junction
  • attaches a variety of cells, including fibroblasts to ECM
  • link to actin filaments of cytoskeleton
  • this type of integrin binding is is reversible
  • -> very important for movement over surfaces
  • can be stable or turn over very rapidly (ex. migrating cells)
29
Q

Hemidesmosomes

A
  • type of cell-matrix junction
  • mediate epithelial cell attachments at which a specific integrin interacts with laminin in the basal lamina
  • link to intermediate filaments of cytoskeleton
  • strongest cell-matrix junction
  • very stable and long-term junctions
30
Q

3 Categories of Cell-Cell Junctions

A
  1. Stable Adhesion Junction
    - adherens and desmosome
  2. Tight Junctions
  3. Gap Junctions
31
Q

Adheren Junctions

A
  • involves a family of integral plasma membrane proteins in adjacent cells (cadherins)
32
Q

Cadherins

A
  • link the actin cytoskeleton of adjacent cells via adheren junctions
33
Q

Desmosomes

A
  • involve a family of cadherins known as desmoglein and desmocollin
34
Q

Desmoglein and Desmocolling

A
  • link the cytoskeletons of adjacent cells via desmosome junctions
35
Q

Tight Junctions

A
  • critically important to the function of epithelial cell sheets (ex. intestinal)
  • form a barrier between fluid compartments
  • -> molecules move across the cell so cell can regulate it
  • separate apical and basal domains of p. membrane
  • -> prevent lateral movement of integral membrane proteins between domains of cell
  • have minimal adhesive strength
36
Q

Junctional Complexes

A
  • a region of cell-cell contact containing a tight junction, adherens junction and a desmosome
37
Q

Gap Junctions

A
  • important for cell-cell (intracellular) communication and coordination of cellular activity
  • open channels through the p. membrane that provide direct connections btwn cytoplasm of adj. cells
  • allow for open flow of ions and other small molecules
  • provide mechanism to couple metabolic and electrical activity of adj. cells
38
Q

Connexin

A
  • member of a family of transmembrane proteins that form gap junctions
39
Q

Connexon

A
  • a cylinder formed by 6 connexions in the plasma membrane

BMSC 220 (6 decks)

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