Cell Adhesion

Question 1

What are the typical components of Intercellular junctions?

Answer 1

Transmebrane adhesive proteins, cytoplasmic adapter protein and cytoskeletal filaments

Question 2

What are the arrangements of inter-celllular junctions?

Answer 2

Macula and zonula

Question 3

what is Macula?

Answer 3

patch-like junction of limited extent

Question 4

what is Zonula?

Answer 4

junction which encircles the entire cell

Question 5

what are the junctional combinations you can have in intercellular junctions?

Answer 5

Junctional Complex (terminal bar) cuboidal or columnar epithelium
Intercalated disc: cardiac muscle

Question 6

what are the types of junctions possible?

Answer 6

Gap, tight an adherens junctions

Question 7

What are the types of adherens junctions? give examples of each

Answer 7

• cells attaching to other cells (adhering junctions and desmosomes)
• cels attaching to/ anchoring in the extracellular matrix (hemiesmosome and focal adhesion)

Question 8

What are Gap Junctions?

Answer 8

plaque-like junctions in which cell membranes of neighboring cells are very close together; intercellular space only 2-3nm

Question 9

Where can Gap junctions be found?

Answer 9

they can be found in basic tissue types and are common in epithelial cells, smooth and cardiac muscle cells, neuronal cells and osteocytes

Question 10

Describe how gap junctions form and work structurally

Answer 10

• 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

Question 11

Is the channel formed by Gap Junctions Hydrophobic or Hyrophillic?

Answer 11

hydrophillic

Question 12

what types of molecules do Gap junctions allow pass?

Answer 12

• 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

Question 13

True or False: all Gap junctions result in the same permeability.

Answer 13

False, different members of connexin family result in differences in permeability

Question 14

What are Tight/ occluding juntions?

Answer 14

• -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

Question 15

Which Transmembrane proteins are involved in Tight Junctions?

Answer 15

• 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

Question 16

what are some cytoplasmic proteins associated with tight junctions:

Answer 16

kinases, transcription factors and cell polarity-related proteins

Question 17

How is permeability determined in tight junctions?

Answer 17

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

Question 18

what are adherens junctions?

Answer 18

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

Question 19

What happens in Adherens junctions when there is loss of contact to adjacent cells or extracellular matrix?

Answer 19

may trigger apoptosis or result in loss of polarity

Question 20

what are cell-to-cell adhesive junctions made of?

Answer 20

• transmembrane adhesive proteins members of cadherin (calcium ion-dependent proteins) family
• cytoplasmic adapter proteins members of the catenin family

Question 21

what are cell-to-ECM adhesive junctions made of?

Answer 21

similar to c2c adhesive junctions but transmembrane proteins members of integrin family (heterodimers with alpha and beta subunits)

Question 22

where can adherens junctions be found?

Answer 22

found basal to tight juntion zonula in epithelial cells

• associated with belt-like band of actin
• encircles entire cell (zonula)

Question 23

what do catenins interact with?

Answer 23

interact with cytoplasmic domain of trans-membrane protein, cytoskeletal proteins an other cytoplasmic proteins

Question 24

what are desmosomes?

Answer 24

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

Question 25

what makes up desmosome?

Answer 25

• 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

Question 26

What composes a junctional complex

Answer 26

1. ) a band of tight junctions (TJ) forming an occluding zone in the top position
2. ) a band of anchoring junctions in the middle position (son-in-law adherens, ZA)
3. ) a circle of spot desmosomes (DES)