Lecture 5: Epithelial Tissues: Cell Adhesion Molecules (CAMs) Flashcards
What are the two components of the basement membrane? What is the origin of each?
Basal lamina; originates from the epithelial tissue
Reticular lamina; originates from the connective tissue
What are the components of the basal lamina?
Laminin, fibronectin, type IV collagen, entactin, and proteoglycans.
What is the major component of the basal lamina? What are its characteristics (structure and function)?
Laminin is the major component.
It consists of three different chains named alpha, beta, and gamma.
It has binding sites for proteoglycans, integrins, entactin, and type IV collagen. (PIE + collagen)
What are the characteristics of fibronectin (structure and origin)? What does it bind to?
It is a protein consisting of two polypeptide chains linked by a disulfide bridge. Cellular fibronectin is produced by fibroblasts and plasma fibronectin is secreted by hepatocytes.
It has binding sites for fibrin, integrins, type IV collagen, and heparin (proteoglycan). (FICH)
What are the calcium dependent CAMs?
Selectins and cadherins (S & C)
What are the calcium independent CAMs?
Integrins and immunoglobulin superfamily molecules (I’s)
Identify the three classes of cadherins and where they are found.
P-cadherins: placenta
E-cadherins: epithelial tissues
N-cadherins: nerve cells
(PEN)
What class of cadherin is the most common?
What disease is associated with the loss of this cadherin in tissues?
E-cadherin
Tumors, specifically metastatic tumors, are associated with the loss of e-cadherin as it allows for the tumor tissue to spread beyond the normal boundaries of the original tissue type.
What is the function of catenin?
It acts as an interface between cadherins and the actin cytoskeleton of the cells they hold together.
What is the structure of selectins?
What do they do and what function group of molecules does this put them in?
They are a protein with an extracellular carbohydrate-recognition domain (CRD) which is activated by nearby calcium binding sites.
They bind specific carbohydrate making them lectins.
Give an example of a process in which both selectins and integrins are used by the body and describe this process.
Extravasation of leukocytes.
Selectins on the the endothelial surface of blood vessels loosely bind leukocytes causing them to roll. Ligands, ICAM-1 and V-CAM1, on the endothelial surface cause the leukocyte to present integrins. Integrin strengthens the binding of the leukocytes to the endothelium and mediates transendothelial migration.
What is the structure and function of integrin?
It is a glycoproteins consisting of two subunit, alpha and beta, of which there are several variants of each.
They connect the cytoskeleton and ECM. They bind to the RGD (Arg-Gly-Asp) sequences of extracellular fibronectin and laminin.
List and compare the three categories of junctional complexes.
Adherens: anchor cells together and reinforce structural integrity of tissues.
Occludens: establishes impermeable barrier which prevents paracellular transport and maintains concentration differences between environments.
Gap junctions: creates pores that allow cells to rapidly exchange ions and small molecules allowing for coordination of activities.
What are the types of junctions?
Zonula: “belt-like” complexes that span the circumference of the cell connecting it to all neighboring cells; associated with actin
Macula: “spot” junctions refered to as desmosomes (lateral domains) or hemidesmosomes (basal domains); associated with intermediate filaments
Describe the molecular structure of zonula adherens.
Two dense, intracellular plaques (associated with catenin complex) linked by cadherins and an afadin-nectin complex. Connects to intracellular actin filaments.
