Lecture 23 of 373: Cell Junctions and Cell Adhesion Molecules (1 hrs : 9 mins) | CUET (Common University Entrance Test) PG Zoology (SCQP28) | Complete Video Course 373 Lectures [222 hrs : 42 mins]

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Cell Adhesion Molecules

Cell adhesion molecules (CAMs) are proteins located on the cell surface involved in the binding of cells with each other and with the extracellular matrix. These molecules are important for the formation of tissues, maintenance of tissue integrity, and the transmission of signals that regulate cell behaviour.

Cell Junctions

Cell junctions are specialized structures that connect adjacent cells or a cell to the extracellular matrix. These junctions play crucial roles in maintaining the structural integrity of tissues, facilitating communication between cells, and regulating the passage of substances.

Adherens Junctions:

They are connected to actin filaments.

Found in epithelial and endothelial tissues.

Main protein responsible is Cadherins (such as E-cadherin). Adaptor proteins are α-Catenin, β-catenin, p120-catenin, vinculin.

Require Ca^{2 +} ions for interaction.

Desmosomes:

They are also type of adherens junction only, but cadherin is desomosomal cadherin (Desmogleins, desmocollins) linked to intermediate filament rather than actin filament.

Prominent in epithelial and cardiac tissues.

Main protein is Desmogleins & desmocollins. Adaptor proteins are plakoglobins, plakophillins & desmoplakins.

Tight junction:

Tight junctions between adjacent epithelial cells are usually located in a band surrounding the cell just below the apical surface.

These specialized junctions form a barrier that seals off body cavities such as the intestinal lumen and separates the blood from the cerebral spinal fluid of the central nervous system (i.e.. , the blood-brain barrier).

Tight junctions prevent the diffusion of macromolecules and, to varying degrees, small water-soluble molecules and ions across an epithelium via the spaces between cells.

They also help establish and maintain the polarity of epithelial cells by preventing the diffusion of membrane proteins and glycolipids between the apical and the basolateral regions of the plasma membrane, ensuring that these regions contain different membrane components.

The two principal integral membrane proteins found in tight junctions are occludin and claudin.

Claudin is essential for forming tight junctions.

Occluding which is not essential for the assembly or structure of the tight junction but is important for limiting junctional permeability.