A cell-cell junction that seals cells together in an epithelium in a way that prevents even small molecules from leaking from one side of the sheet to the other.

Area of closely apposed plasma membranes of two adjacent animal cells; lateral diffusion of proteins within the lipid bilayer is reduced and intercellular exchange of solutes is enhanced.

Found near the apical surface of cells in simple epithelia. Forms a sealing "gasket" around the cell by the fusion of adjacent cell membranes which encircle the apical cell surface like a belt or fence. Prevents fluid moving through the intercellular gap and the lateral diffusion of intrinsic membrane proteins between apical and basolateral domains of the plasma membrane as well as occludes the movement of solute molecules between cells. Various proteins components of this junction have been identified, but how they are linked to form the ultrastructure of the junction is not known.

Cell-cell junctions that seal adjacent epithelial cells together, preventing the passage of most dissolved molecules from one side of the epithelial sheet to the other. (Alberts et al., Molecular Biology of the Cell, 2nd ed, p22)

(bicellular tight junction) An occluding cell-cell junction that is composed of a branching network of sealing strands that completely encircles the apical end of each cell in an epithelial sheet; the outer leaflets of the two interacting plasma membranes are seen to be tightly apposed where sealing strands are present. Each sealing strand is composed of a long row of transmembrane adhesion proteins embedded in each of the two interacting plasma membranes.