Cell Junction, Cell adhesions & Extracellular Matrix (Sept. 9-Denning) Flashcards
List the 2 main types of tissue involved in cell junctions
1) Epithelial tissue
2) Connective tissue
What are the characteristics of epithelial tissue
- Low ECM & High # cells
- Cells are tightly bound together in sheets
- Cells bear most of the mechanical stress through junctional complexes that attach to the cytoskeleton.
List the characteristics of connective tissue
- High ECM & Low # of cells
- Matrix is rich in fibrous polymers (e.g., collagen)
- Matrix bears most mechanical stress
List the 5 main types of cellular junctions and their particular functions
1) Occluding: Seal cells so nothing can pass in between (tight junctions)
2) Cell-Cell Anchoring: Connects lateral walls of cells together (Actin & Adherens/IFs & desmosomes)
3) Channel-Forming: Allows selective transport of materials between cells (gap junctions)
4) Cell-Matrix Anchoring: Links together cell and ECM (actin/focal adhesions or hemidesmosomes/IFs)
5) Signal-Relaying junctions: Neurotransmitter secretions
Describe the function of claudins and occludins in tight junctions
- Claudins are 4-pass transmembrane proteins.
- Found at lateral surface just below apical surface of cell.
- Prevent paracellular transport
- Occludins serve similar function, but are found in significantly less number
T/F: Glucose can normally pass between epithelial cells of the intestine
False: tight junctions prevent leaking and transportation of molecules between cells. Glucose uses Na+ symporter to move and undergo transcellular transport
What is the function of anchoring junctions?
- Stabilize cells against mechanical stress
- Mechanically attach cells and their cytoskeleton to their neighbors or to the extracellular matrix
For the 4 subtypes of anchoring proteins, list the (1) type, (2) transmembrane adhesion protein, (3) cytoskeletal attachments
1) Adherens (cell-cell) - cadherin - actin
2) Desmosome (Cell-cell) - cadherin (desmoglein) - IF
3) Focal adhesions (Cell-matrix) - integrin - actin
4) hemidesmosomes (cell-matrix) - integrin - IF
What is the function of cadherin?
Cadherins are transmembrane adhesion proteins that work to form cell-cell junctions between filaments via anchor proteins
What is the adhesion belt in adherens junctions?
Join an actin bundle in one cell to actin bundle in adjacent cell
Form adhesive belt just below tight junction
What ion does cadherin require for assembly?
Ca2+
Where are desmosomes typically found?
Between cells. They function as “spot welds”
They are anchored to IFs via desmosomal cadherins and plaque proteins
What are the functions of focal adhesions?
- Link the cell to ECM
- Allows cell to hang on to surroundings (think leucocyte rolling)
Focal adhesions bind to \_\_\_\_ via the transmembrane protein \_\_\_\_\_\_ (A) actin; integrin (B) microtubules; integrin (C) intermediate filaments; cadherin (D) desmosomes; actin
(A) Focal adhesions are connected to actin via anchoring proteins and use integrins (transmembrane ECM binding proteins) as the interacting subunits
List the (1) function, (2) transmembrane protein that mediates the connection, and (3) the final end connection of hemidesmosomes
1) Distribute forces on an epithelium to the basal lamina
2) Integrins mediate basal lamina adhesion
3) Anchor proteins link integrins to intermediate filaments
Describe the phenomenon that is cadherin dependent sorting?
Homophilic binding of cadherin dimers favors association of like cadherin dimers. This binding allows the eventual separation and distinct cell types aggregating together which allow tissue homeostasis and sorting of similar cell types
What are selectins?
Selectins are Lectins: Carbohydrate binding proteins
They are transient, calcium-dependent adhesion molecules
which exhibit heterophilic binding and are connected to integrins