How do gap junctions differ from tight and adherens/desmosomes in epithelial tissue function?

How do gap junctions differ from tight and adherens/desmosomes in epithelial tissue function?

• A. They facilitate paracellular transport of large molecules.
• B. They anchor cells to each other via cadherins.
• C. They allow direct cytoplasmic exchange of ions and small molecules between cells via connexins.
• D. They seal cells to prevent movement of substances.

Answer: (C)

Gap junctions create channels that directly connect the cytoplasm of neighboring epithelial cells, made from connexin proteins that dock to form a continuous pore. This allows ions and small molecules—like calcium, ATP, and cyclic messengers—to pass freely between cells, enabling quick electrical and metabolic synchronization across the tissue. Tight junctions, in contrast, act as a seal between cells to restrict paracellular movement; they don’t provide channels for cytoplasmic exchange. Adherens junctions and desmosomes use cadherin-based adhesion to link cells to the actin cytoskeleton or intermediate filaments, providing mechanical strength, but they do not form cytoplasmic channels either. So the defining feature of gap junctions is this direct cytoplasmic exchange via connexin-formed channels, which sets them apart from the barrier role of tight junctions and the adhesive, structural roles of adherens/desmosomes.