3. Hemi-desmosomes are structure found between
(1) Two adjacent plant cells
(2) Two adjacent animal cells
(3) Between cell and extracellular matrix
(4) Within a bacteria

What Are Hemidesmosomes?

Hemidesmosomes are specialized, multiprotein complexes that play a pivotal role in anchoring the basal side of epithelial cells directly to the underlying basement membrane, a crucial component of the extracellular matrix. These structures fortify tissue resilience and help maintain the integrity and stability of epithelial layers exposed to constant mechanical stress, such as in the skin and other mucosal surfaces.​

Structure of Hemidesmosomes

The architecture of hemidesmosomes is elaborate and tailored for anchoring:

• Located at the basal surface of epithelial cells, hemidesmosomes are characterized by their electron-dense plaques within the cell, which connect to intermediate filaments in the cytoskeleton.​

• The key adhesion molecules include integrin α6β4, which functions as a receptor for laminin-332 in the basement membrane.​

• The cytoplasmic plaque comprises proteins such as plectin, BP230, and BP180, which link intermediate filaments to the plasma membrane and, through transmembrane components, to the extracellular matrix.​

• These anchoring junctions provide the tightest adhesive interactions between cells and their extracellular environment in animal tissue.​

Hemidesmosomes: The True Location

Not Between Two Adjacent Cells

Hemidesmosomes do not connect adjacent cells directly. Instead, they connect the basal domain of an epithelial cell to the underlying basement membrane, which is a major part of the extracellular matrix.​

Not Within Plants or Bacteria

There are no hemidesmosomes between two adjacent plant cells or within bacteria. Plant cells use structures like plasmodesmata for interactions, and bacteria lack these specialized junctions.​

Function and Importance

Hemidesmosomes are critical for:

• Anchoring Epithelial Cells: They provide strong, stable adhesion between cells and the extracellular matrix, particularly reinforcing areas subjected to abrasion and mechanical stress, such as skin, cornea, and mucosal epithelia.​

• Protecting Tissue Integrity: By joining the cell cytoskeleton to the basement membrane, hemidesmosomes maintain tissue architecture and prevent separation or blistering.​

• Disease Relevance: Defects in hemidesmosome components, such as integrins or plectin, are implicated in blistering diseases like bullous pemphigoid, illustrating their importance for tissue stability.​

Key Facts Summary

Hemidesmosome Molecular Composition

• Integrin α6β4: Central to adhesion, binding to laminin in the basement membrane.​

• BP230 and BP180: Bullous pemphigoid antigens, linking plaque proteins to the cytoskeleton and extracellular matrix.​

• Plectin: Crosslinking intermediate filaments, essential for the integrity of the plaque.​

These molecular links anchor the cell securely to the matrix, enabling the tissue to withstand mechanical wear.

In Summary

Hemidesmosomes are critical structures that anchor epithelial cells to the basement membrane of the extracellular matrix, ensuring the integrity and resilience of animal tissues exposed to mechanical stress. This makes statement (3), “Between cell and extracellular matrix,” the correct answer.