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o Certain cells need to be able to contact other nearby cells. Cell junctions adhere membranes of adjacent cells.
Types of Cell Junctions
There are three different types of cellular junctions:
I. Gap Junctions
o Connect the cytoplasm of adjacent cells, which allows for the movement of molecules between the cells.
o Gap junctions are found in the heart muscle. Gap junctions allow for rapid spread of information between cells.
o Ex. Electrical synapse
Diagram Representing Types of cell Junctions
II. Tight Junctions
o Provide waterproof seals between adjacent cells to prevent leakage of fluid.
o Tissues held together by tight junctions may act as a complete fluid barrier.
o Tight junctions also act as a barrier to protein movement between the apical and basolateral surface of a cell.
o The portion of the cell exposed to the lumen is called its apical surface.
o The rest of the cell (i.e., its sides and base) make up the basolateral surface.
o The lumen is the space enclosed by an organ/organelle.
o Tight junctions perform two vital functions:
o They prevent the passage of molecules and ions through the space between cells.
o So materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue.
o This pathway provides control over what substances are allowed through.
o They block the movement of integral membrane proteins (red and green ovals) between the apical and basolateral surfaces of the cell.
o Thus the special functions of each surface, for example o receptor-mediated endocytosis at the apical surface o exocytosis at the basolateral surface can be preserved.
III. Adhering Junctions (Desmosomes)
o Join two cells at a single point and they directly attach the cytoskeleton of each cell.
o They don’t prevent fluid from circulating around all sides of a cell.
o Are the types of junctions found cells that experience a lot of stress and they often accompany tight junctions.
o Ex. in epithelial cells which allow for stretching.
o Desmosomes (adhering junctions) act like spot welds.
Cell Junctions Citations
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