Characteristics Of Epithelial Tissues Practice Test

Tight junctions are organized as a belt around epithelial cells and are called the zonula occludens. Their sealing function comes from transmembrane proteins called claudins and occludins that interact with those on neighboring cells to form a near-impermeable barrier to paracellular diffusion. Inside the cell, scaffold proteins such as ZO-1 anchor these transmembrane components to the actin cytoskeleton, stabilizing the junction and helping organize the membrane domains. This combination of sealing proteins plus cytoskeletal links defines the tight junction complex. Other junctions use different proteins and serve different roles—desmosomes rely on cadherins for strong cell–cell adhesion, gap junctions on connexins for intercellular communication, and hemidesmosomes on integrins to attach cells to the basement membrane.