Glossary of 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
- 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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