Cell junctions

Question 1

Why are junctions formed

Answer 1

• seal spaces between cells
• allow communication
• mechanical strength

Question 2

what are anchoring junctions

Answer 2

connect together cytoskeletons of individual cells by transmembrane liner proteins

Question 3

What are the two types of anchoring junctions

Answer 3

Adherens and desmosomes

Question 4

What are Adherens junctions

Answer 4

streak-like attachments in non-epithelial cells and continuous belts in epithelial
Highly dynamic and involved in epithelial sheet folding

Question 5

What is the structure of Adherens junctions

Answer 5

• catenins - intracellular membrane proteins
• Ceherins - intercellular linker proteins
• actin filaments - cytoskeleton filament (attached to catenins)

Question 6

What are desmosomes

Answer 6

Very strong cell adhesions
Look like buttons
Between epithelial cells that undergo significant mechanical stress

Question 7

How can things go wrong with desmosomes

Answer 7

Can have serious pathological affects since they join tissues undergoing high stress e.g. cardiac cells
autoantibodies can cause a potentially fatal blistering disorder.

Question 8

What is the structure of desmosomes

Answer 8

• Desmoplakin - intracellular membrane proteins
• Cadherins - transmembrane linker proteins
• intermediate filaments (joined to Desmoplakin)

Question 9

Communicating (Gap) junctions

Answer 9

look like a patch where membranes are slightly separated
Have clusters of protein channels for direct diffusion between cells

Question 10

Occluding (tight) junctions

Answer 10

seal membranes of adjacent cells through network of proteins

Question 11

What are the functions of occluding junctions

Answer 11

• prevent substance movement in intermembrane space
• prevent leakage of water-soluble molecules between cells
  prevent movements of proteins and lipids within membranes
• defines boundary between apical and basolateral surfaces

Question 12

what are cell-EMC junctions

Answer 12

• transmembrane proteins to directly connect cytoskeleton and EMC
• integrin mediated focalised adhesions to actin filaments allowing cell to adhere substrates to it and then they can migrate along it

Question 13

What is an example of a cell EMC junction

Answer 13

e.g. keratinocytes (in skin) - bind to intermediate filaments to plectin to make them strong

Question 14

What is cell polarity

Answer 14

Asymmetrical organisation of different components in parts of the cell allowing cells to have specialised functions in different domains of the cell

Question 15

What is the basal surface

Answer 15

contact and connected with basal membrane
sometimes involved in ion transport

Question 16

What is the apical (luminal surface)

Answer 16

contacts exterior
can have specialised surfaces like microvilli or cilia