Cell Junctions Flashcards
four classes of cell junctions
anchoring
occluding
channel forming
signal relaying
anchoring junctions
control cell to cell adhesions and cell matrix adhesion
connected to cytoskeletal inside the cell
actin filament attachment cites in anchoring junctions
either adherens or actin linked cell matrix adhesions
intermediate filament attachment sites in anchoring junctions
desmosomes
hemidesmosomes
occluding junctions
seals gaps between cells so that epithelium is impermeable barrier
channel forming junction
creates passage way for small molecules and ions to pass from cell to cell
signal relay junction
allows signals to be related from cell to cell across their plasma membrane at cell to cell contact
list of type of junctions on slide 99
top to bottom
tight junction
adherents junction
desmosomes
gap junction
then on floor is actin linked cell matrix adhesion and hemidesmosome
list junction types from apical to basal
occluding
cell to cell anchoring
channel forming
cell matrix anchoring
what is an example of homophillic adhesion?
catenins
highly selective recognition in tight junctions
cadherins are __ dependent and bind to ___
calcium dependent, bind to like (homophillic adhesion)
what links classical cadherins to cytoskeleton
B-catenin, p120 catenin, y-catenin
2 superfamilies of cadherin
classical
nonclassical
classical cadherins
main mediators of Ca2+ dependent junctions
E cadherin (most) (epithelial cells, brain) N cadherin (muscle, nerve, lens) VE cadherin (endothelial cell P cadherin (placenta)
nonclassical cadherins
include desmocollins and desmogleins that form desmosome junctions
True or false?
none of the adhesion molecules are bound directly to cytoskeleton
true
they all must have linker proteins on cytoplasmic side (i.e. catenins)
tight junctions
exclude molecules from apical and basal side so that they can selectively pass
- barrier funciton
- fence function
- signaling function
what anchors tight junctions to actin cytoskeleton
Zo
what anchors adherent to eptiheleium
adhesion belt
molecules involved in polarity
downstream of cadherins coming together
Par
Crumbs
Scribble
what type of junctions has size restrictions?
gap junction
allows ions and very small molecules (i.e. glucose)
1000 Daltons (1 kD)
what are the proteins that make up gap junctions?
connexins
connexins
make up gap jxns
continually removed and replaced
can be same (homo) or different (hetero)
basal lamina is made of
laminin
collagen type IV
bidirectional signaling
information can flow from extracellular in or intracellular out
this is a characteristic of basal lamina
focal adhesions
link ECM to thru integrin receptor to actin cytoskeleton
if unstable – nascent
focal contacts
sites in the ECM, integrins, and cytoskeleton interact
FAK
cytoplasmic tyK
recruited by talin or pazillin and provide docking site for Src kinase
extraceulluar macromolecules of matrix
GAGs
fibrous proteins
GAGs
covalently linked to proteins to form proteoglycans – ground substance
fibrous proteins
collagen and fibronectin
structural and adhesive
Laminin
primary organizer of sheet structure
classical laminin (a, b, y)
type Iv
tensile strength to basal lamina
superhelix of 3 proteins
what links laminin and Type IV collagen?
nidogen and perlecan
integrins
span membrane with short C terminal tail and long N terminal
bind to form cytoskeleton
integrins
utilize laminin and type IV
dimeric
they’re the anchor to the basal lamina
activation of integrins requires what protein?
focal adhesion kinase
inside out activation
intracellular signals cause talon to move to a-b linkage, integrin is active
signal to integrin can come via
outside (substrate)
inside (signal)
what type of cells make up ECM?
fibroblasts
GAGs
big squishy part of ECM
lubricate and connect things
HUGE proteoglycans
sugars connected to proteins connected to another protein
hyaluronic acid
long stem on the GAGs
building block
highly hydrated, takes up lots of space
squishy
collagen
all the cross linking takes place in ER
fibroblasts ER is where collagen assembly takes place
what is essential for the affinity of collagen fibers?
Poly/Lysl hydroxylases
for all the pro filaments really
defects of these enzymes or lack of the substrates