CAMs & Junctional Complexes Flashcards
what are characteristics of the basement membrane
separates an epithelial layer from its connective tissue support
is approximately 50-88nm thick
2 components: basal lamina and reticular lamina
What are the 2 components of the basement membrane and what are they produced from
Basal lamina: produced by the epithelium
Reticular lamina: produced by the connective tissue
define the basement membrane
extracellular component in direct contact with the basal domain of epithelial cells
what are characteristics of laminin
major component of basal lamina: consists of 3 chains (alpha, beta, gamma)
has binding sites for integrins, type IV collagen, entactin & proteoglycans
what are the characteristics of fibronectin
protein made up of 2 polypeptide chains cross-linked by disulfide bonds
forms: cellular and plasma
has binding sites for: Heparin, Integrins, Collagen, Fibrin
decipher between plasma fibronectin and cellular fibronectin
plasma is produced by hepatocytes and secreted into the bloodstream; cellular is produced by fibroblasts and forms part of the extracellular matrix
what are the 2 calcium dependent CAMs
cadherins
selectins
what are the calcium independent CAMs
integrins
immunoglobulin superfamily molecules
what ligands do cadherins recognize and what are the stable types of junctions
ligands: other cadherins
junctions: occludes and desmosomes
what ligands do selections recognize and what are the stable types of junctions
ligands: carbohydrates
junctions: none
what ligands do integrins recognize and what are the stable types of junctions
ligands: extracellular matrix molecules
junctions: hemidesmosomes
what ligands do Ig Superfamily recognize and what are the stable types of junctions
ligands: integrins
junctions: none
what are the 3 types of classical cadherins and where are they found
E: found in epithelial tissues
N: found in nerve cells
P: found in placenta
what are the types of non-classical cadherins and where are they found
desmocollins and desmogleins
found in desmosomes
what is the most common type of cadherin?
E-cadherin
what is the loss of e-cadherin associated with
invasive behavior of tumor cells
how do E-cadherins form dimers
via a HVA binding face (Histidine-Valine-Alanine sequence)
what are catenins?
small proteins that link the cytoplasmic end of cadherin with cytoplasmic actin
what are the 3 forms of catenins & what do they do
B and gamma plakoglobin catenins: attach to cytoplasmic end of cadherin, Beta may also serve as a transcription cofactor, Beta is also attached to alpha catenin
Alpha: Binds directly to cytoplasmic actin (interface between cadherin and actin cytoskeleton)
What serves as a major interface between the cadherins that hold adjacent cells together and the actin cytoskeletons of those cells
Catenins
what are characteristics of selectins
bind to carbohydrates (belong to lectin group)
involved in the movement of leukocytes from blood to tissues
what are the 3 main classes of selections and what are they associated with
P: associated with platelets
E: associated with activated endothelial cells
L: associated with leukocytes
what are characteristics of integrins
- they are glycoproteins that are mainly involved in cell-extracelllular matrix interactions
- bind to both extracellular matrix and cytoskeleton
- 2 subunits: one alpha (17 kinds) and one beta (8 kinds)
- Extracellular domains of integrins bind to molecules in the extracellular matrix such as fibronectin and laminin
- interact with the RGD (Arg-Gly-Asp) sequence in fibronectin and laminin
what do the laminin and fibronectin in the basement membrane interact with
collagen
heparan sulfate proteoglycans
entactin
what are characteristics of the alpha-subunit of integrins
has 2 chains linked by disulfide linkage and a globular head with binding sites for divalent cations
what are characteristics of the Beta-subunit of integrins
- the extracellular chain contains repeating cysteine-rich regions
- the intracellular portion interacts with actin filaments through 3 connecting proteins: talin, vinculin, an alpha-actinin
define the Ig superfamily
Members of this family posses an extracellular segment with one or more folded domains characteristic of immunoglobulins
What are some members of the Ig superfamily
- N-CAM: mediate both hemophilic and heterophilic interactions
- I-CAM-1 & I-CAM-2: I-CAM-1 facilitates transendothelial migration of leukocytes (migration of leukocytes from blood vessels to surrounding tissue)
Define Adherens
- Molecular complex that anchor cells together and reinforce the physical integrity of tissues and the cells that make up the tissues (found on the basolateral surfaces of epithelial cells)
- characterized by intercellular spaces which are filled with cadherin proteins
Define occludens
Molecular complexes that establish an impermeable barrier between adjacent cells, especially epithelial cells, that prevent paracellular transport and maintains concentration difference between the environments on either side of the epithelial sheet (if cells are not help together, occludes are worthless)
Define gap junctions
Composed of molecular pores that enables cells to rapidly exchange ions and small molecules that help coordinate activities among the cells that make up the tissue
- communicating junction that allows cells to directly communicate
- composed of connexins
Define and characterize Zonula
- can be either adherents or occludens
- travel all the way around the circumference of the cell and link all neighboring cells to the central cell. Sometimes called belt-like complexes
- associated with intracellular actin
Define and characterize Macula
*spot or snap-like junction
of adherents variety and are often referred to as desmosomes (associated with lateral domain of epithelial cells) or hemidesmosomes (associated with the basal domain of epithelial cells)
* associated with intracellular intermediate filaments (tonofilaments)
Define Hemidesmosomes
anchoring junctions that anchor the basal domain of the epithelial cell to the basal lamina
what does a hemidesmosome consist of
- cytoplasmic plate associated with intermediate filaments (such as keratin)
- membrane plaque linking the hemidesmosome to the basal lamina via anchoring filament and integrins
what doe the zoluna occludes proteins and afadin facilitate interaction with
intracellular actin filaments
Define tight junctions
circumferential belts at the apical domain of epithelial cells and linking adjacent endothelial cells. They seal the space between epithelial cells and regulate the passage of water and flux of ions between adjacent epithelial cells.
Define Focal Adhesions
- spots that anchor the cell to the extracellular matrix via integrins
- Differ form desmosomes in that the intracellular attachment is not to tonofilaments such as keratin but to actin filaments via connecting proteins
define the intercellular channel
axial channel that allows the direct passage of small signaling molecules between adjacent cells to coordinate cell responses
The basal lamina is associated with which type of collagen?
type IV
Which type of CAM is associated with the zonula occludes and desmosomes
Cadherins
Desmocollins and desmogleins belong to which of the following groups of CAMs
cadherins
which of the following serves as a major interface between the cadherins that hold adjacent cells together and their actin cytoskeletons
catenins
The extracellular domains of which of the following bind to molecules in the extracellular matrix such a fibronectin and laminin
Integrins
which molecular complex anchors cells together and reinforce the physical integrity of tissues and the cells that make up the tissues
Zonula adherens
Which molecular complex primarily serves to prevent paracellular transport
zonula occludens
