Cell Adhesion Flashcards
What are the typical components of Intercellular junctions?
Transmebrane adhesive proteins, cytoplasmic adapter protein and cytoskeletal filaments
What are the arrangements of inter-celllular junctions?
Macula and zonula
what is Macula?
patch-like junction of limited extent
what is Zonula?
junction which encircles the entire cell
what are the junctional combinations you can have in intercellular junctions?
Junctional Complex (terminal bar) cuboidal or columnar epithelium Intercalated disc: cardiac muscle
what are the types of junctions possible?
Gap, tight an adherens junctions
What are the types of adherens junctions? give examples of each
- cells attaching to other cells (adhering junctions and desmosomes)
- cels attaching to/ anchoring in the extracellular matrix (hemiesmosome and focal adhesion)
What are Gap Junctions?
plaque-like junctions in which cell membranes of neighboring cells are very close together; intercellular space only 2-3nm
Where can Gap junctions be found?
they can be found in basic tissue types and are common in epithelial cells, smooth and cardiac muscle cells, neuronal cells and osteocytes
Describe how gap junctions form and work structurally
- integral memebrane protein is connexin
- 6 connexin make a connexon which has a central channel w/ a diameter of 2nm
- connexons of one cell connect to connexons in adjacent cell to form hydrophillic channel
- tens to hundreds of aligned connexon pairs hexagonnally packed in a gap junction
Is the channel formed by Gap Junctions Hydrophobic or Hyrophillic?
hydrophillic
what types of molecules do Gap junctions allow pass?
- aqueous channels are between the cytoplasm of adjacent cells
- allows for the passage of small signaling molecules and ions
- connected cells are electrically coupled for coordinated responses to stimuli
True or False: all Gap junctions result in the same permeability.
False, different members of connexin family result in differences in permeability
What are Tight/ occluding juntions?
- -anastomosing strand of adhesive transmembrane proteins
- linear series of contacts to proteins of adjacent cell
- intercellular space obliterated at contact site; junction encircles entire cell
- found close to the apical end of cuboial or columnar epithelial cells
Which Transmembrane proteins are involved in Tight Junctions?
- members of claudin family, occludin, junctional adhesive molecule
- transmembrane adhesive proteins interact homotypically with proteins in adjacent cell
- some cytoplasmic proteins: kinases, transcription factors, cell polarity-related proteins
- actin filaments associated
what are some cytoplasmic proteins associated with tight junctions:
kinases, transcription factors and cell polarity-related proteins
How is permeability determined in tight junctions?
depends on the number of junctional strands, their completeness and type of adhesive protein
-movement of ions and small moecules in intercellular space prevented/ controlled
- movement of membrane proteins limited
efinition of cell domains (apical vs basolateral)
cell adhesion
what are adherens junctions?
cells held together or attached to/ anchored in the extracellular matrix
- the intercellular space between attached cells: 20nm wide at location of adhesive junction
- they are commonly involved in (intra) cellular signaling (e.g for nuclear transcription, tumor suppression, differentiation)
- contribution to adhesive force between on cell and another
What happens in Adherens junctions when there is loss of contact to adjacent cells or extracellular matrix?
may trigger apoptosis or result in loss of polarity
what are cell-to-cell adhesive junctions made of?
- transmembrane adhesive proteins members of cadherin (calcium ion-dependent proteins) family
- cytoplasmic adapter proteins members of the catenin family
what are cell-to-ECM adhesive junctions made of?
similar to c2c adhesive junctions but transmembrane proteins members of integrin family (heterodimers with alpha and beta subunits)
where can adherens junctions be found?
found basal to tight juntion zonula in epithelial cells
- associated with belt-like band of actin
- encircles entire cell (zonula)
what do catenins interact with?
interact with cytoplasmic domain of trans-membrane protein, cytoskeletal proteins an other cytoplasmic proteins
what are desmosomes?
disk-shaped adhesive juntions (macula)
- foun basal to zonula adherens in epithelia cells in band encircling cell as welll as scattered over lateral cell surface
- common in many tissues
- intercellular space (30nm) filled with highly-ordered proteins
- attachement site for strong cytoskeletal components (intermediate filaments)
- provides firm adhesion among cells
what makes up desmosome?
- transmembrane ahesive proteins (cadherins): desmoglein, desmocollin
- cytoplasmic adapter proteins (catenins): desmoplakin, plakoglobin, plakophilin
- cytoskeletal element: intermediate filaments (anchoring in catenin plaque); type depends on tissue
What composes a junctional complex
- ) a band of tight junctions (TJ) forming an occluding zone in the top position
- ) a band of anchoring junctions in the middle position (son-in-law adherens, ZA)
- ) a circle of spot desmosomes (DES)
