BSC 2.8 (Cell Junctions)

Cell Junctions and Surfaces

Presentation to environment: Defense mechanisms: Maintain structure. Cells-Tissues-Organs: Allow communication between cells

Plant Cell Walls

Flexible primary wall is later enforced by more rigid secondary walls: Area between cells is filled with middle lamella (Contains pectin): Plasmodesmata are channels between cells that allow cytoplasm exchange

Animal Cell Junctions

Tight junctions connect cells together and block “seepage” of extracellular fluids: Adherens junction connects the cytoskeletons of two adjacent cells via cadheren proteins": Desmosomes anchor adjacent cells together structurally (linked to intermediate filaments): Hemidesmosomes anchor cells to connective tissue (Integrin proteins make connection: Gap junctions allow molecules to pass from cell to cell (comparable to plasmodesmata in plants)

Cadherins

Protein: Spans cell membrane: Binds to cytoskeleton inside of cell: Binds to another cadherin outside of cell

Integrins

Protein: Spans cell membrane: Binds to cytoskeleton inside of cell: Binds to connective tissue like fibronectin, collagen, and laminin outside of cell

Extracellular Matrix

Many types of glycoproteins (form branched complexes): Fibronectins act as docking site (Bound to integrins): Integrins span membrane and are bound to cytoskeleton: Molecules in extracellular matrix determine properties of tissue

Roles of ECM

Give tissue stability by linking areas of cells together: Allows communication between: ECM is essential in development