cell junctions

structure of connective tissue

cells separated by extracellular matrix

function of extracellular matrix

directly bears mechanical stress and tension

what are the 5 main types of epithelial tissue

simple, stratified, squamous, columnar, cuboidal

apical

facing external environment - air or fluid

basal

facing basement mem

the basalateral surface of epithelial cells is attached to what ?

basal lamina

what are the 3 functional classes of cell junction ?

occluding, anchoring, communicating

what are the 3 anchoring junctions ?

adherens desmosomes and hemidemosomes

function of tight junctions

diffusion barrier between fluid compartments - seal neighbouring cells in epithelial sheet to prevent leakage of extracellular molecules

what 3 transmembrane proteins form tight junctions ?

occludin claudin JAM1

the intracellular tails of occludin and claudin are bound to…

zona occludins

zona occludins are attached to…

actin filaments

role of occludin

binds to adjacent cell sealing paracellular pathway

occuldin is composed of how many transmembrane proteins ?

4

role of JAM-1

maintains cell polarity

what does the larger first extracellular loop of claudin determine ?

tightness and selective ion permeability

where are tight junctions found in excess ?

blood-brain barrier, GIT, kidneys

what specialised type of tight junction is found in the epithelial sheets of kidneys and why ?

leaky - allows for movement of certain ions

function of adherens junctions

resist shearing forces and tension

adherenes junctions are composed of what type of molecule ?

cadherins

what proteins bind cytosolic cadherin tails to actin ?

beta catenin, p120 and alpha catenin

what would be the result of a mutation in the genes coding for E-cadherin ?

disrupted cell adhesion - cells growing on top of each other (cancer) and metastasis of cancer

role of Ca2+ in adherens junctions

fill gap between 2 cadherin molecules

how do desmosomes compare to adherens junctions ?

stronger - denser plaque of intracellular adaptor proteins

the non-classical caherins of desmosomes are linked to…

intermediate filaments eg.keratin

where are desmosomes found in excess ?

cardiac tissue

the combination of desmosomes and GAP junctions between cardio myocytes are called…

intercalated discs

what is the function of hemidesmosomes ?

anchors cell to basal lamina

what is the transmembrane glycoprotein hemidesmosomes contain called ?

integrin

what is the function of GAP junctions ?

allow for cell communication

what molecules travel via GAP junctions ?

ions and small molecules eg. proteins

a connexon is composed of…

6 connexins

between what cells would you find GAP junctions in excess ?

smooth muscle, cardiac

which junction connects intermediate filaments of one cell with another ?

desmosomes

how many human connexin proteins are there ?

21

which junction connects actin filament bundles in adjacent cells ?

adherens