Cell Junctions Flashcards
What are cell junctions ?
Contact points between plasma membrane of tissue cells.
Functions of tight junctions ?
They inhibit the passage of substances between cells and prevent the contents of these organs from leaking into the blood and surrounding tissues.
Structure of tight junctions
Weblike strands of transmembrane proteins that fuse together the outer surface of adjacent plasma membrane to seal of passageways between adjacent cells.
Examples of tight junctions
Cells of epithelial tissue that lines the stomach, intestines and urinary bladder.
Functions of adherens junction ?
Help epithelial surfaces resist separation during various contractile activities.
Example of when adherens junction occur?
Intestines - when food moves through
Structure of adherens junction
Contain plaque - dense layer of proteins on the inside of the plasma membrane that attaches both to membrane proteins and microfilaments of the cytoskeleton. Transmembrane glycoproteins called cadherins join the cells.
Function of desmosomes
Prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction.
Examples of desmosomes use
Epidermal cells (outermost layer of the skin) and cardiac muscle cells.
Structure of desmosomes
- and difference in structure to adheren junctions
Plaqua and transmembrane glycoproteins (cadherins) extend into intercellular space between adjacent cell membrane and attach cells to one another.
Difference to adherens is that plaque does not attach to microfilaments but rather intermediate filaments - which consist of protein keratin.
What accounts for the stability of the cells and tissue in relation to the structure of desmosomes ?
Intermediate filaments extend from one side of the cell to the opposite side of the cell - going through the cytosol.
Function of gap junctions
Ions and small molecules can diffuse through the cytosol of one cell to another but passage of large molecules such as vital intracellular proteins cannot.
- Allow cells to communicate with each other
- Transfer of nutrients and even waste (in avascular tissue - leans and cornea of the eye)
- Enable nerve or muscle impulses to spread quickly
Structure of gap junctions
Membrane proteins called connexins form tiny fluid filled tunnels called connexons that connect neighboring cells.
Narrow intercellular gap between plasma membranes.
Ions and small molecules travel through the connexons.
