Cell Junctions Flashcards
What are the 6 major cell junctions?
- Tight junctions (AKA occluding junctions)
- Gap junctions
- Desmosomes
- Adherins junctions
- Hemidesmosomes
- Focal adhesions
What are the functions of tight junctions?
- Seals gap between epithelial cells to prevent passing of molecules between cells
- Induces variable permeability
Where are tight junctions distributed?
Found in all epithelia tissue
What is the major protein vital for formation of tight junctions?
Claudins
What are 2 proteins, other than claudins, involved in tight junctions? What do they both do?
- Occludin - limits junctional permeability
2. Tricellulin - seals cell membranes together
Are gap junctions uniform in size?
No
What do gap junctions allow?
Regulated, direct cell-cell communication
What are gap junctions made up of?
Connexins and innexins
allows ions through but not protein, mRNA etc.
What is the function of gap junctions?
Creates direct channels between adjacent cells to allow passage of small, water-soluble molecules from cell to cell
What factors regulated gap junctions?
- pH
- Calcium ions
- Voltage difference between two cells
Why do calcium ions potentially close gap junctions?
To limit damage caused from excess calcium ions
What are adherins junctions made from?
E cadherin
Adherins junctions are _____-dependent
Ca^2+
What kind of interaction does E cadherin have?
Homophilic, E cadherin only binds to E cadherin
How are cadherins associated with the cytoskeleton?
Cadherins are bound to catenins which are bound to actin filaments of the cytoskeleton
What is the function of adherins junctions?
Connects actin filaments in one cell with that of another to join cytoskeletons of adjacent cells
Where are adherins junctions distributed?
- Epithelial tissues
- Heart where they anchor actin bundles on the contractile apparatus and link contractile cells end-to-end
What structure do asherins junctions produce in epithelial cells? What does this structure allow for?
Adhesion belts AKA belt desmosomes, a continuous connection of actin filaments beneath apical surface of epithelia
Co-ordinated contraction of this belt allows for processes such as invagination and formation of tubes in morphogenesis
In simple terms what do adhesion belts allow the conversion of?
Conversion of sheet of cells into a tubule
What is the function of desmosomes?
Connect intermediate filaments in one cell to those in the adjacent cell to provide mechanical strength
Which proteins do desmosomes use?
Similar cadherins
Which junction do desmosomes connect?
Cell-cell
What is the function of hemidesmosomes?
Anchor intermediate filaments in a cell to the extracellular matrix
Which junction do hemidesmosomes connect?
Junction between cell and basal lamina of ECM
What is the function of focal adhesions?
Anchor actin filaments in a cell to the extracellular matrix
What is the transmembrane adhesion protein in both hemisdesmosomes and focal adhesions?
Integrins
What is a clinical condition caused by the dysfunction of desmosomes? How does it cause its symptoms?
Pemphigus
Produces antibodies against a desmosome cadherin called desmoglein, causes skin blistering
