Cracking the AP Biology Exam

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Cells

CELL JUNCTIONS

When cells come in close contact with each other, they develop specialized intercellular junctions that involve their plasma membranes as well as other components. These structures may allow neighboring cells to form strong connections with each other, prevent passage of materials, or establish rapid communication between adjacent cells. There are three types of intercellular contact in animal cells: desmosomes, gap junctions, and tight junctions.

Desmosomes hold adjacent animal cells tightly to each other, like a rivet. They consist of a pair of discs associated with the plasma membrane of adjacent cells, plus the intercellular protein filaments that cross the small space between them. Intermediate filaments within the cells are also attached to the discs (see figure below).

Gap junctions are protein complexes that form channels in membranes and allow communication between the cytoplasm of adjacent animal cells or the transfer of small molecules and ions.

Tight junctions are tight connections between the membranes of adjacent animal cells. They’re so tight that there is no space between the cells. Cells connected by tight junctions seal off body cavities and prevent leaks.