Cell Adhesion 3 - Cell-cell Junctions

Question 1

What is the role of tight junctions?

Answer 1

Stitch cells together

Question 2

What is the role of adhesions journey?

Answer 2

Join actin filaments to neighbouring cells

Question 3

What is the role of desmosomes?

Answer 3

Join intermediate filaments to neighbouring cells

Question 4

What is the role of hemidesmosomes?

Answer 4

join intermediate filaments to the basal lamina

Question 5

What is the role of gap junctions?

Answer 5

form tunnels of aqueous connectivity between cells

Question 6

Explain the structure of adhering junctions

Answer 6

• cadherins proteins
  (calcium-dependent adherence proteins)
• linking the cytoskeleton of adjoining cells - mechanical stress
• cadherins bind directly onto each other (homophilic binding)
• Ca2+ needs to be present for this binding

Question 7

Where are adherins junctions normally found?

Answer 7

• near apical surface underneath tight junctions

Question 8

what are adhesion belts?

Answer 8

• makes belts of actin across the epithelium

Question 9

what is the role of adhesion belts?

Answer 9

• can change shape and get tension due to actin and myosin
• if contracts over one axis - tube
• if contracts along multiple axis - sphere / vesicle
• important for forming the neural tube and lens vesicle

Question 10

What is spina bifida?

Answer 10

• failure of the neural tube to close
  leads to:
• abnormalities of the spinal chord
• neurological deficits (motor/sensory function)

Question 11

Explain desmosomes

Answer 11

• connect keratin filaments in neighbouring epithelial cells
• keratin is an intermediate filament (type of cytoskeleton)
• another type of transmembrane cadherins connect the plasma membranes together
• keratin provides structure to the cell
• also called spot welds

Question 12

Explain hemidesmosomes

Answer 12

• connects epithelial cells to the basal lamina
• integrins in the epithelial cell membrane connects keratin filaments in the cell to the basal lamina
• other end of the integrins are bound to keratin via linking proteins

Question 13

What is epidermolysis bullosa (EB)?

Answer 13

genetic skin condition causing blisters and lesions
- gene therapy can be done to correct defect in mutant gene

Question 14

Explain gap junctions

Answer 14

• when cells are very close together
• allow transfer of small intracellular water soluble molecules (up to 1kDa)
• connexion protein complexes line up to form water filled channel between two cells

Question 15

What is a connexon?

Answer 15

• protein made of 6 subunits
• line up to form gap junctions

Question 16

Explain gap junctions permeability

Answer 16

• gap junctions are gated
• what gets through is determined by extracellular signals

Question 17

Explain gap junction permeability in retinal neurons

Answer 17

• gap junctions close in response to dopamine
• more light - dopamine releases
• this switches the retina from using rod (low light) to cone photoreceptors (bright light)

Question 18

Explain plasmodesmata

Answer 18

• plants do not have tight junctions, adhering, desmosomes and hemidesmosomes as they have a cell wall to create structure
• these carry out the role of gap junctions
• smooth ER between cells