Cytoskeleton and Cell Junctions

Tight Junctions
- Function: Seals neighboring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them; helps polarize cells.
- Acts as a barrier, preventing water or other molecules from moving from the apical side to the basal side of epithelial sheets.
- Create a seal in epithelial sheets.
- Made of two proteins:
  - Claudins
  - Occludins
Adherens Junctions
- Function: Joins an actin bundle in one cell to a similar bundle in a neighboring cell.
- Provide mechanical strength.
- Allow a sheet of cells to change shape, which is important for developmental processes.
- Link cells via actin filaments.
- Made of cadherin.
  - Cadherins are transmembrane proteins.
  - Cadherins from neighboring cells link together outside the cell.
  - Link to actin filaments inside the cell.
Desmosomes
- Function: Joins the intermediate filaments in one cell to those in a neighbor.
- Use cadherin to link cells via intermediate filaments.
- Provide mechanical support to cells.
Gap Junctions
- Function: Forms channels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites, to pass from cell to cell.
- Formed by connexons
- Create open channels between neighboring cells.
- Allow exchange of water, ions, and small molecules between cells.
Hemidesmosomes
- Function: Anchors intermediate filaments in a cell to the basal lamina.