4BBY1030 - CELL ADHESION

what is extracellular matrix

network of extracellular macromolecules such as collagen, enzymes and glycoproteins - provide structural and biochemical support of surrounding cells

what is extracellular matrix made up of

basement membranes - thin, fibrous tissues that separate epithelia, mesothelial and endothelia and the fibrillar matrix which is 3D and contains collage i, fibronectin, elastin and proteoglycans

what is the basement membrane made up of

basal lamina - secreted by epithelial cells - composed of laminin and collagen type 4 and reticular lamina - connective tissue secreted by reticular cells - thin branching structure of collagen type 3

cell adhesion

where cells adhere

cell junction

structures which enable cell adhesion

desmosomes

- pairs of dark disk button structure at cell-cell contacts

1. helps connect cells to each other

hemisdesmosomes

link cells to the ECM eg the basal lamina, 1. connects cells to the basal lamina

2. desmosomes and hemidesmosomes anchor intermediate filaments inside the cell

3. intermediate fiber networks of adjacent cells are indirectly connected to, one another through desmosomes and to basal lamina through hemidesmosomes - this mechanically strengthens the entire epithelial tissue

4. defects of the intermediate fibers, desmosome, hemidesmosome or basal lamina could lead to fragility of skin or other epithelia.

tight junction

- surrounds apical circumference of cell that sits tight like a headband

- its function is to be a fence - controls flow direction -apical and basolateral membrane proteins cannot diffuse beyond

- be a barrier - keeps molecules in the body and block harmful ones

gap junctions

- canal/pores between cells - controls permeability

- they form pores penetrating neighbouring cells

- only ions and small molecules can pass through

adherents junction

- sits under the tight junction

- squeezes cells due to underlying actomyosin bundle

- provides mobile force for epithelial folding

- maintain cell to cell adhesion in epithelial cells

e-cadherin

main component of adherent junctions, causes cell sorting

ca2+ alters the cadherin structure and activity

also component of desmosomes

integrins

component of hemidesmosomes

focal adhesion

connects cell to ECM

1. Integrin ( transmembrane protein ) binds to ecm outside of cell

2. connected to actin filaments by linker proteins - inside plasma membrane

3. can generate movement

4. pivotal to force transduction and migration of cells