Cell junctions Flashcards
What is the function of the extracellular matrix?
Give strength to supportive tissue
Collagen
Function:
- Gives strength to CT to resist stretching
- Most abundant protein in the body
- The long, stiff triple-stranded helical structure
Divided into Collagen molecule, collagen fibrils, collagen fibers, pre-collagen
Made by fibroblasts (osteoblasts in the bone) from the extracellular matrix
Integrins and fibronectin
Is involved in adhesion of cells to each other and their substrate. Helps attach a cell to the ECM.
Fibronectin is an extracellular matrix protein.
Integrins in the plasma membrane bind to collagen fibrils.
Glycosaminoglycans (GAG´s)
Function:
- Resist compression
- Filters to regulate the passage through the ECM
- Bind secreted growth factors
- Can block, encourage or guide cell migration through the matrix
Are negatively charged polysaccharide chains made of repeating disaccharide units.
Form the gelly like substance in the eye -> “space fillers”
Hydrophilic
Epithelial sheets
Divided into:
- Simple
- Stratified
- Columnar
- Cuboidal
- Squamos
Laminin
Provide adhesive sites for integrin molecules + a linking role
IKKE det samme som Lamins
Tight junctions
Sealing function
- Serve as barriers to solute diffusion so that water-soluble molecules cannot easily leak between two neighbouring cells.
- Prevents diffusion of protein within the plasma membrane
- Sites for assembly for the complexes of intracellular proteins
Formed by Claudins and Occludins
Maintaining the polarity of the individual epithelial cell
Adherens junctions
- Cytoskeleton-linked junctions that bind epithelial cells to one another and to the basal lamina
- Mechanical strength
- ## Built around transmembrane proteins belonging to the cadherin family
Desmosome
A different set of cadherin molecules connect to keratin filaments.
Bundles of ropelike keratin filament criss-cross the cytoplasm and are spot welded to the bundles of keratin filaments in adjacent cells.
- Gives strength
Gap junctions
A direct channel of communication from cell to a neighboring cell.
The membrane is penetrated by a protein assembly called connections. (formed by 6 subunits).
Two connections joined across the cellular gap to form an aqueous channel. connecting the cytosol of the two cells.
Gap junctions can in many cells be open or closed in response to extra or intracellular signals.
Cadherin
Function:
Linking cells to each other
Bound with homophilic binding (one identical cadherin in one cell is bound to another identical-looking cadherin in another cell.
Important for embryonic development (neural tube)
Hemidesmosome
A structure that looks like half a desmosome, where the integrin tail is linked to keratin filaments
