In which cell-surface junction fused membrane reveals five-layered structure?

Options

A. Desmosomes
B. Zona occludence
C. Gap-junction
D. Plasmodesmata

Answer

**Step-by-Step Solution:**

1. **Understanding Cell-Surface Junctions**: Cell-surface junctions are specialized structures that connect adjacent cells. They play crucial roles in maintaining the integrity and function of tissues.

2. **Identifying the Junction Types**: The main types of cell-surface junctions include tight junctions, desmosomes, gap junctions, and plasmodesmata. Each type has distinct structural features and functions.

3. **Focus on Tight Junctions**: Among these junctions, tight junctions are known for their ability to form a barrier that regulates the passage of substances between cells. They are particularly important in epithelial tissues.

4. **Examining the Structure of Tight Junctions**: When a cross-section of a tight junction is observed, it reveals a unique five-layered structure. This is due to the fusion of the membranes of adjacent cells.

5. **Key Proteins Involved**: Two important transmembrane proteins are involved in the formation of tight junctions: occludin and claudin. These proteins help to seal the space between cells, contributing to the five-layered appearance.

6. **Terminology**: Tight junctions are also referred to as "zona occludens" due to their occlusive nature, which prevents the passage of molecules and ions through the intercellular space.

7. **Conclusion**: Therefore, the cell-surface junction that reveals a five-layered structure upon cross-section is the tight junction, also known as zona occludens.

**Final Answer**: The junction is the tight junction (zona occludens).

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