Cell-Cell Junctions: Videos & Practice Problems

Cell-cell junctions are crucial for connecting cells and maintaining tissue integrity. The main types include:

• Adherens Junctions: Use cadherins to anchor cells to actin filaments, providing mechanical stability.
• Desmosomes: Link epithelial cells via intermediate filaments, offering strong adhesion.
• Tight Junctions: Formed by claudins or occludins, they prevent leakage of water and ions between cells.
• Gap Junctions: Allow communication through connexins, enabling the passage of water and inorganic ions between cells.
• Plasmodesmata: Connect plant cell cytosols, facilitating communication and transport of substances.

Tight junctions are crucial for maintaining cell polarity by creating a barrier that separates the apical and basal surfaces of epithelial cells. They are formed by proteins such as claudins and occludins, which create a seal that prevents the mixing of membrane proteins and lipids between these two regions. This separation ensures that specific functions are localized to the correct cellular regions, such as nutrient absorption on the apical side and signal transduction on the basal side.

Cadherins are essential proteins in both adherens junctions and desmosomes. In adherens junctions, cadherins link to actin filaments, providing mechanical stability and facilitating cell-cell adhesion. In desmosomes, cadherins connect to intermediate filaments, offering strong adhesion between epithelial cells. These interactions are crucial for maintaining tissue integrity and enabling cells to withstand mechanical stress.

Gap junctions facilitate direct cellular communication by allowing the passage of water, ions, and small molecules between adjacent cells. They are formed by connexins, which create channels that align between neighboring cell membranes. This connectivity enables the rapid transfer of signals and nutrients, essential for coordinated cellular activities, such as muscle contraction and neural signaling.

Plasmodesmata and gap junctions both facilitate intercellular communication, but they differ in structure and function. Plasmodesmata are found in plant cells and connect the cytosol of adjacent cells through channels in the cell wall, allowing the transport of molecules and ions. Gap junctions, on the other hand, are found in animal cells and consist of connexin proteins that form channels between cell membranes, enabling the passage of small molecules and ions. While both are crucial for cellular communication, their structural differences reflect their adaptation to plant and animal cells, respectively.