L24 - Cell-cell junctions

Question 1

What are the 4 types of cell junctions?

Answer 1

1. Tight Junctions - seals the gap between epithelial cells
2. Cell-cell anchoring junctions
   - adherens junction connects actin filament bundle in one cell with that in the next cell
   - desmosome connects intermediate filaments in one cell to those in the next cell.
3. Channel forming junctions - gap junction allows the passage of small-water soluble molecules from cell to cell.
4. Cell - matrix anchoring junctions
   - actin-linked cell-matrix adhesion anchors actin filaments in cell to extracellular matrix
   - hemidesmosome anchors immediate filaments in a cell to extracellular matrix.

Question 2

Explain Adherens junctions (and focal adhesion)

Answer 2

They are both actin-linked junctions.

Adherins junctions make strong links between cells.

e.g Cadherins - which are Ca 2+ dependent and have a homophobic interaction - it links to actin cytoskeleton which helps anchor the junction.

Question 3

What is the role of Hemidesmosomes?

Answer 3

Attach cells to Basal lamina
- intergrins and intermediate filaments

INTEGRIN - FOCAL ADHESION - HEMIDESMOSOME

Question 4

what is the role of desmosomes?

Answer 4

Desmosomes give cell-cell jucntions.

• Cadherins and Intermediate Filaments
• Plentiful in heart muscle and epidermis.

CADHERIN - ADHERENS JUNCTION - DESMOSOME

Question 5

What is the location and role of tight junctions?

Answer 5

Location - epithelia - e.g gut

Roles:

• To prevent fluid, ion and membrane flow
• Variable Extent
• Transcellular transport
• Paracellular Transport.

Question 6

Describe the structure of Gap juctions

Answer 6

• 100-500nm long
• Gap = 2-4 nm
• Allows regulated and direct cell-cell communication
• Forms 1.5nm diameter pores.
• Made of connexins