Which feature of tight junctions prevents substances from leaking between cells?

Tight junctions function as barriers that prevent the passage of substances between cells, and their distinctive structure is crucial to this role. They are formed by strands of proteins that weave together to create a seal, resembling the way a zipper fastens two sides together. This zipper-like closure effectively blocks the space between neighboring cells, ensuring that any substances must go through the cells themselves rather than slipping between them. This is essential for maintaining the integrity of tissues, particularly in places such as the intestinal epithelium and blood-brain barrier, where controlled transport of materials is vital.

In contrast, increased permeability would allow substances to leak through, channel formation would create pathways for transport rather than sealing the space, and structural support does not address the barrier function specifically. Thus, the zipper-like organization of the proteins in tight junctions is what primarily establishes their capability to prevent leakage between cells.