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Biochemistry Cell Junctions and ECM
Cell Junctions and ECM of Epithelial Cells and Basal Lamina
34
Biology
Graduate
08/21/2010

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Cards

Term
Actin Filaments
Definition

Cytoskeleton

At cell periphery along PM

Maintain cell shape

Cell-cell contact and signaling

[image]

Term
Intermediate Filaments
Definition

Throughout cytoplasm

Attach to basal membrane

Mechanical strength

[image]

Term
Microtubules
Definition

Throughout cytoplasm

Molecular trafficking

[image]

Term
Adherens Junctions
Definition

Connect actin cytoskeleton of neighboring cells

Use classical cadherins (E-cadherin)

Lateral side of cell

[image]

 

Term
Desmosome
Definition

Structural stability

Connect IF of neighboring cells

Use desmoglein and democollin to bind to keratin in cell

Withstand tearing and shearing forces

Lateral side of cell

[image]

Term
Attachment protein for adherens junction
Definition
Classical cadherins-E cadherin
Term
Attachment Protein for Desmosome
Definition
Desmoglein and Desmocollin
Term
Tight Junctions
Definition

Molecular trafficking: inhibits flow of molecules around cell

Can allow paracellular transport by loosening junctions

Claudin and occluden proteins

[image]

Term
Gap Junction
Definition

Channels for molecules to flow between cells

Regulate electrochemical, chemical, and metabolic coupling

6 transmembrane proteins (connexins) make 1 connexon

Can open and close if cell damaged/ sick

Term
Proteins forming Tight Junctions
Definition

Claudin

Occluden

Term
Proteins forming Gap Junctions
Definition
6 connexins make 1 connexon
Term
Basal Lamina
Definition

Tough, flexible sheet of fibrous proteins

Under epithelium...provides anchor to CT

(1) laminin

(2) type IV collagen

(3) glycoproteins 

-fibronectin

Term
Laminin
Definition

Large and flexible protein in basal lamina

3 interwoven polypeptides linked by disulfide bonds

Head groups bind each other or collagen to form sheet-like network

[image]

 

Term
Type IV Collagen
Definition

Found in basal lamina

3 protein strands loosely packed

N and C termini bind to one another or laminin to form mesh

[image]

Term
Fibronectin
Definition

Epithelial cell adherence to basal lamina

V-shaped with 2 polypeptides joined with disulfide bonds

Can bind integrins, collagen, proteoglycans (heparin)

[image]

Term
Glycoproteins
Definition
Found in basal lamina
Term
How to link epithelium to basal lamina
Definition

(1) focal contact

(2) hemidesmosome

Term
Focal Contact
Definition

Link between epithelium and basal lamina

Use actin

Bind to collagen and fibronectin with integrin proteins

Term
Hemidesmosome
Definition

Link epithelium to basal lamina via IF

Bind to laminin using integrins

Term
Integrin
Definition

Transmembrane protein that binds to ECM proteins

Anchors epithelial cells

Dimer of alpha and beta

Term
Components of ECM of basal lamina
Definition

(1) collagen fibrils

(2) elastin

(3) proteoglycans

Term
Collagen fibrils
Definition

Type I and II

Tough--mechanical strength

Hydroxylation and crosslinking

Term
How to form a collagen fibril?
Definition

(1) pro-alpha-chain spooled into ER lumen

(2)hydroxylate proline and lysine

(3) glycosylation 

(4) 3 pro-alpha-chains make a procollagen

(5) export procollagen to ECM

(6) cut procollagen loose ends--tropocollagen

(7) tropocollagens make a fibril

Term
Pro-alpha-chain
Definition

Synthesized by epithelial cells

Will become collagen fibril

Term
Procollagen
Definition

Formed from 3 pro-alpha-chains

Will become collagen fibril

[image]

Term
Tropocollagen
Definition

Formed when secreted procollagen has loose end removed

Will become collagen fibril

[image]

Term
Prolyl hydroxylase
Definition

proline-->hydroxyproline

Requires Vit C

Hydroxyproline, proline, and glycine allow tropocollagen to make fibrils

Term
How to make hydroxylysine
Definition

lysine-(lysyl hydroxylase, Vit C)->hydroxylysine-(lysyl oxidase)->stable tropocollagen crosslinks

 

unstable crosslinks from lysyl oxidase only

 

Term
Scurvy
Definition

Lack of Vit C--hydroxylases do not function making weak collagen fibrils since crosslinking in tropocollagen is weak

Unable to endure mechanical stress

Most sensitve: periodontal ligament and gingiva (remade often)

Term
Elastin
Definition

Component of basal lamina

Skin, blood vessels, lungs 

Hydrophobic monomers with extensive crosslinking

Molecular spring

[image]

Term
Ground Substance
Definition

Component of basal lamina

Surrounds fibrous proteins

Carbohydrate rich, hydrated gel

Made of 

(1) hyaluronic acid

(2) adhesive glycoproteins

(3) proteoglycans--GAG

Term
Proteoglycans
Definition

Part of ground substance

Core proteins linked covalenty via serine to polysaccharide chains of glycosaminoglycans (GAG)

[image]

Term

Glycosaminoglycans

GAG

Definition

Part of proteoglycans (ground substance)

Disaccharide repeats (amino sugar and acidic sugar)

Too stiff to be globular so form extensive expansion which attracts water and fills ECM

Sugars are sulfated and/or carboxylated

Negative charge attracts Na+ which attracts water-->molecular cushion (compression and nutrition to nonvascularized areas)

4 groups

(1) hyaluronan

(2) chondroitin sulfate

(3)heparan sulfate

(4) keratan sulfate

Term
Hyaluronan
Definition

Longest GAG, part of proteoglycan-ground substance

Non-sulfated but still negative

not covalently linked to core protein, forms backbone of proteoglycan

 

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