Cell junctions

Question 1

What is the function of the extracellular matrix?

Answer 1

Give strength to supportive tissue

Question 2

Collagen

Answer 2

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

Question 3

Integrins and fibronectin

Answer 3

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.

Question 4

Glycosaminoglycans (GAG´s)

Answer 4

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

Question 5

Epithelial sheets

Answer 5

Divided into:

• Simple
• Stratified
• Columnar
• Cuboidal
• Squamos

Question 6

Laminin

Answer 6

Provide adhesive sites for integrin molecules + a linking role
IKKE det samme som Lamins

Question 7

Tight junctions

Answer 7

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

Question 8

Adherens junctions

Answer 8

• 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

Question 9

Desmosome

Answer 9

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

Question 10

Gap junctions

Answer 10

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.

Question 11

Cadherin

Answer 11

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)

Question 12

Hemidesmosome

Answer 12

A structure that looks like half a desmosome, where the integrin tail is linked to keratin filaments