Adjacent cell membranes sometimes cooperate to form junctions, which are ordered arrays of specialized membrane proteins. The locations on the cell surface where cells of a tissue adhere to one another are called cell junctions. Intercellular junctions are typically classified into three groups, which vary physically in their molecular composition and ultrastructural appearance, and functionally in the degree to which they couple adjacent cells:Adhering Junctions
Click here for picture.
Organizing Junctions
Organizing cell junctions partition the plasma membrane into separate compartments. Tight junctions are belts of proteins that prevent any membrane proteins afloat in the lipid bilayer from drifting across the boundary from one side of the cell to the other. Tight junctions link epithelial cells together into sheets and function to restrict permiability across the sheet.
Click here for picture.
Communicating Junctions
Communicating cell junctions called gap junctions pass small molecules from one animal cell to another. Such passageways are large enough to permit the passage of small molecules, such as sugar molecules and amino acids, from one cell to another, but small enough to prevent the passage of larger molecules, such as proteins. Gap junctions form pores between cells that allow chemical and electrical coupling, thus facilitating intercellular communication
Click here for picture.