L7. Cell Junctions Flashcards
What are the 4 different tissue types in the body?
- epithelium
- connective
- muscle
- nervous
What are cell junctions
allow the formation of tissues by connecting cells with other cells
Where are cell junctions most prominent?
epithelium cells
What locations can cell junctions be in a cell?
- cell-cell interaction
- cell-ECM interaction
What types of cell junctions are there ( 3 types)
- occluding ( sealing)
- anchoring
- channel-forming
Purpose of the occluding junctions
seal the contacts between cells
Purpose of the anchoring junctions
mechanically attach cells together
Purpose of the channel forming junctions
allows chemical and electrical junctions to pass through the cells
What are the 3 main types of proteins in adhesion complexes? State their characteristics
- Adaptor protein : allow recruitment of additional components to adhesion proteins, regulate adhesion complex
- Transmembrane adhesion protein: spans the cell membrane
- cytoskeletal linkers: physical link between adhesion complex and cytoskeletal linkers
Draw the full adhesion complex protein
L7 pg 4b.
Name the 4 cell-cell junctions
- zonular adherins ( anchoring )
- tight junctions ( sealing)
- desomosomes ( anchoring)
- gap junctions ( communicating)
Name the 2 cell-ECM junctions
- focal contacts ( anchoring)
2. hemidesosomes ( anchoring)
What are polarized cells
cells that have specialized domains
What are the 3 sides of the of the epithelial cell
- basal
- lateral
- apical
Draw where the 4 cell-cell junctions are in a polarized cell
L7 pg 6a
What composes the junctional complex?
the occluding junctions and anchoring junctions ( ie. desmosomes, tight junctions and zonular adherins)
What are the 3 ways that anchoring junction proteins resist the large force of the cell?
- multi-protein complex: redundancy
- cluster of adhesion proteins: combined strength
- link to cytoskeleton (adhesion protein) : large tension bearing protein interaction
What is freeze fracture used for?
look at junctional proteins
State the process of freeze fracture
- cells are frozen
- frozen cells are fractured, fracture is irregular
- thin layer is sprayed on surface to produce cast
- organic material is digested by acid- leaving replica
- replica is examined
What is the E-face
inner face of the outer lipid monolayer
What is the P-face
inner face of the inner lipid monolayer
What is another name for tight junctions?
zonular occludens
How are tight junctions formed
tight junctions formed through transmembrane protein interaction
What are the 2 proteins that make up the tight junctions?
claudin and occludin
Describe claudin
- needed for tight junction formation
- 4-pass transmembrane protein
Describe occlaudin
4-pass transmembrane protein receptor
barrier function
not needed for maintaining tight junction structure
What is the function of tight junction
controls solute diffusion between body compartment (eg. glucose transport into blood-glucose blocked by diffusing between the cells -tight junctions, want to actively transport glucose through plasma membrane transporters )
What happens when claudin 16 is lost
problem with tight junction
calcification in kidney
disrupt electrolyte cleaning
another name for zonular adherens
adheren junctions
What do adheren junctions form?
continuous adhesion belts
2D sheets of cells
What makes adheren junctions/ zonular adherens?
cadherins (adhesion protein)
transmembrane protein
What do adheren junctions link to
actin filaments
how many pass is an adheren junction
single pass
What is the structure of adherin junctions ( draw structure)
the cadherin cluster together (L7. pg 14a)
How do adherin junction form?
cadherin molecules bind to other cadherins (aggregate)
cadherin extracellular domain straiten with calcium binding
cadherin cis-homodimer straightening allows trans homodimerization
what is a trans homodimer
when (cadherin) molecule binds another molecule on the surface of ANOTHER cell
what is a cis homodimer
when (cadherin) molecule binds another molecule on the surface of the same cell
What are catenins?
They are adaptor proteins(INTRACELLULAR anchoring complex) that link the cadherin homodimers to the actin cytoskeleton
draw relation between catenin, actin filaments and cadherins
(L7, pg 15b)
What happens when cadherins are lost
tumor
What is the alternative name of desmosomes
macula adherens
What is the adhesion bases for desmosomes
-desmocolin and desmoglein ( cadherin like receptors)
Which cytoskeletal element do desmosomes bind to
intermediate filaments (keratin family)
What are desmosomes used for
strengthening tissue
Where are desmosomes found
tissues exposed to tensile forces
Draw the relation between cytoskeleton, intermediate filaments, dsc dsg ,linkers
pg 17 a
What is pemphigus vulgaris
loss of dsg : skin blistering
What are gap junctions for
allows cells to communicate and share nutrients
Aside from epithelial cells where else are gap junctions formed
cardiomyocyte
smooth muscle
What makes up gap junctions
connexin: gap junction protein
connexon: cluster of 6 connexins
What is Vohwinkel Syndrome (keratodema)
Skin is hard and thick
loss of connexin 26
