L5 - cell adhesion and junctions Flashcards
define cell junction
the structures that enable cell adhesion (junctional complexes)
how many types of cell junctions are there
6
name the types of cell junctions (junctional complexes)
- desmosomes/hemidesmosomes (2)
- tight junctions
- gap junctions
- adherens junction
- focal adhesions
name the two types of extracellular matrices
- basement membrane (basal lamina)
2. fibrillar matrix
what is the basal lamina
type of ECM
a 2D sheet that epithelial cells sit on
what is the fibrillar matrix
type of ECM
3D matrix composed of various fibres, in
which cells such as fibroblasts are buried
what are main components of basal lamina
collagen IV
laminin
nidogen
perlecan
what type of cell junction are desmosomes
cell - cell anchoring junctions
main components of the fibrillar matrix
Collagen I
Fibronectin
Elastin
Proteoglycans
describe appearance of desmosomes
pairs of dark disk like structures at cell - cell contacts
function of desmosomes
connect cell - cell
anchor the intermediate filaments of adjacent cells (indirectly) to eachother
provide mechanical strength
describe appearance of hemidesmosomes
appear like half desmosomes
half disk like structures at the cell - ECM junction
what type of cell junction are hemidesmosomes
cell - matrix anchoring junctions
function of hemidesmosomes
connect cell - ECM
anchor the intermediate filaments of cells to the ECM
mechanical strength
what type of cell junction are tight junctions
occluding junctions
what type of cell junctions are gap junctions
channel - forming junctions
what type of cell junction are focal adhesions
cell - matrix anchoring junctions
what type of cell junction are adherens junctions
cell-cell anchoring junctions
describe appearance of tight junctions
a point where two membranes of cells come together with no gap
located closer to apical side
surround entire cell like a headband
function of tight junctions
- act as ‘fence’ apical and basolateral TRANSMEMBRANE proteins cant diffuse between tight junctions, so the apical ones are kept on the apical side and the basolateral ones on the basolateral side so they can carry out their correct functions
- also act as a permeability barrier for molecules in EC fluid
describe appearance of gap junctions
a point where two membranes of cells come together with a gap - lateral surface
function of gap junctions
canal between cells allowing movement of ions and small molecules when open
where is adherens junction located
beneath tight junctions like another headband
main component of adherens junction
cadherin
function of adherens junction
maintain cell - cell adhesion - cell reassembly
involved in contraction (during epithelial folding)
function of cadherins found in adherens junction
homotypic adhesion that causes cell sorting
how is the adherens junction involved in contraction (leading to epithelial folding)
Cadherins in AJ are linked to the circumferential actomyosin bundle that contracts during epithelial folding
this squeezes the ‘headband’ of cell
results in folding - to form tubes etc
what are focal adhesions
large multimolecular assemblies that contain integrins and attach cell to ECM
how do focal adhesions attach to ECM
integrins of focal adhesions bind to ECM outside the cell and connect to actin filaments inside the cell
where are focal adhesions located
basal membrane
function of focal adhesions
involved in exerting force and movement of cells
differences between hemidesmosomes and focal adhesions
hemidesmosomes connect too IF , FA connect to AF
HD resist force , FA exert force
HD anchor to matrix , FA move on matrix
where is the fibrillar matrix located
under basal lamina
