Cell Adhesion Molecules and Junctional Complexes Flashcards
What is the basement membrane?
It separates the epithelial layer from connective tissue and consists of the basal and reticular lamina.
What is the basal lamina?
The layer of the basement membrane in contact with epithelial tissue. It is produced by the epithelium and contains collagen and other glycoproteins.
What is the reticular lamina?
The layer of the basement membrane under the basal lamina. It contains type III collagen.
What are some components of the basal lamina?
laminin, fibronectin, type IV collagen, entactin and proteoglycans.
What produces type IV collagen?
epithelial cells.
What is laminin?
the major component of the basal lamina; it has binding sites for integrins, type IV collagen, entactin and proteoglycans.
What is fibronectin?
A protein made up of two polypeptide chains cross-linked by disulfide bonds. It can be cellular or plasma and has binding sites for heparin, integrins, collagen and fibrin.
What are the two types of cell-adhesion molecules?
calcium independent and calcium dependent.
What are the calcium dependent CAMs?
cadherins and selectins
What are the calcium independent CAMs?
integrins and immunoglobulin superfamily molecules.
What do cadherins join?
the internal cytoskeleton of a cell and the exterior of another cell.
What do adherins join?
The internal cytoskeleton of a cell and the extracellular matrix.
Where are E-cadherins found?
epithelial tissue
What do E-cadherins form, and where are they found?
dimers that bind to calcium; they are found at the tip of extracellular end of cadherin molecule.
What is the function of E-cadherin?
maintenance of most epithelial layers; it relies of calcium to do so or else the cells will break down.
What are catenins?
small group of proteins that link the cytoplasmic end of a cadherin with actin.
What is the function of cadherins?
To mediate a link with actin, interact with regulatory molecules of actin cytoskeleton and to control adhesive state of EC domain of cadherins.
Catenins are the major interface between what two things?
Cadherins that hold adjacent cells together and the actin cytoskeletons of the cells.
What are selectins?
calcium dependent CAMs that bind to carbohydrates (receptor is for a specific one).
What family do selectins belong to?
lectin (group that binds carbohydrates).
What are selectins involved in?
The movement of leukocytes from blood to tissues.
What are the classes of selectins?
P-selectins (platelets/immune response), E-selectins (endothelial cells); L-selectins (leukocytes).
What are integrins?
Glycoproteins that are mainly involved in cell-extracellular matrix interactions.
Where do integrins bind?
to the extracellular matrix and the cytoskeleton (fibrin and laminin).
What CAM molecules does integrin bind to in the cytoskeleton?
Fibronectin and laminin
What do laminin and fibronectin interact with?
Collagen, heparan, entactin
What are immunoglobulins?
calcium-INdependent CAM; it is the extracellular segment of a CAM.
What are the five types of junctional complexes?
adherens, occludens, gap junctions, zonula and macular
What are adherens?
junctional complex that anchors cells together and reinforces the physical integrity of tissues. They are found on the basolateral surfaces.
What are occludens?
junctional complex that establishes impermeable barriers between adjacent cells to prevent transport and maintain concentration differences.
What are zonula?
junctions (either adherens or occludens) that line the circumference of a cell and link all neighboring cells to a central cell.
What are macula?
junctions (adherens) that are like “spots” that are between the basolateral OR basal domains of cells.
What are desmogleins?
cahderin proteins in the junctions (adherens). They are found in the epidermis. They are linked to the cytoplasm via desmoplakin and plakoglobin.
What are zonula adherens?
Associated with actin microfilaments.
What are the macula dherens?
associated with intermediate filaments (tonofilaments).
What are hemidesmosomes?
Anchoring unctions that anchor the basal domain of the pithelial cell to the basal lamina.
What is the zonal occludens?
A belt-like junction that prevent paracellular transport.
What are tight junctions?
circumferential belts at the apical domain of epithelial cells and linking adjacent endothelial cells.
What are focal adhesions?
Spots that anchor the cell to the extracellular mateix via integrins.
How are adhesions different from desmosomes?
Adhesions attach to actin filaments via connecting proteins and desmosomes attach to tonofilaments, such as keratin.
What are gap junctions?
A communicating junction that allows cells to directly communicate. They are composed of connexons.
What are connexons?
They are what gap junctions are composed of. They facilitate movement of molecules.
When do gap junctions close?
When calcium concentrations are high.
What is the function of a gap junction?
regulate calcium concentration, chemical and electrical coupling.
