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Micro - Cell Junctions


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where does freeze fracture cut between?
between plasma membrane?
what is the P-face of freeze fracture?
replica of inner leaflet

backed by Protoplasm
what is the E-face of freeze fracture?
replica of outer leaflet

backed by Extracellular Fluid
where is the zonula occludens found?
as part of the junctional complex

most apical
what is the zonula occludens made up of?
sealing strands, which are rows of intramembraneous particles that encircle the cell

they are composed of "occludin" and "claudins" and link to actin filaments
what does the zonula occludens look like on freeze fracture?
it looks like ridges on the P face and grooves in the E face
where is the zonula adherins found?
as part of the junctional complex; only in epithelia
what is the zonula adherins made up of?
bundle of actin filaments anchored to intracellular attachment proteins

looks like a fuzzy plaque
what do the components of the junctional complex look like on EM?
zonula occludens: fusion of mbns

zonula adherins: 15-20 nm space in between, with fuzzy plaque

desmosome: 20-30 nm space, dark attachment plaques on the cytoplasmic sides, with dark intercellular space
what is a fascia adherins?
it is similar to the zonula adherins, but in cardiac muscle
what are desmosomes?
spot-like welds holding cells together
where are desmosomes found?
in epithelia as part of junctional complex


and in some non-epithelia
what are desmosomes made of?
intermediate filaments anchored into attachment plaques
what is pemphigus vulgaris?
autoimmune disease against own desmosomes, causing blisters, fluid loss, and infections
what is a hemidesmosome?
anchors basal plasma mbn of epithelial cells to basal lamina of ECM
what is a hemidesmosome composed of?
intermediate filaments, w/ integrin transmembrane proteins
what is bullous pemphigoid?
disruption of hemidesmosomes, causing separation of the epithelium from the basal lamina
where are focal contact/ focal adhesion plaques found?
in fibroblasts, some epithelial cells, smooth muscle
what are focal adhesion plaques?
points where stress fibers (bundles of ACTIN filaments and myosin II) anchor into plasma mbn
what are the transmembrane linker proteins in focal adhesion plaques?
integrins, which bind to fibronectin in the ECM and bind to intracellular attachement proteins (talin and vinculin) that bind to actin filaments
what are the transmembrane linker proteins in desmosomes?
cadherins (e.g. desmogleins, desmocollins)
what are the transmembrane linker proteins in hemidesmosomes?
integrins and collagen XVII
what are the transmembrane linker proteins in zonula adherins?
what are focal adhesion plaques important in?
important in cell movement and wound healing
where are gap junctions found?
epithelia, smooth and cardiac muscle, nerve, and bone
what are gap junctions composed of?
hundreds of paired mbn channels called CONNEXONS, which are bound end to end
what is a connexon?
paired mbn channel made up of a hollow tube of 6 connexins
what are gap junctions used for?
communicating; cell-signaling and exchange of molecules
what do gap junctions look like on EM?
plasma mbns of 2 cells parallel and close (2-4 nm), but not fused
what do gap junctions like on freeze fracture?
IMPs of uniform size and crystalline order

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