Desmosomes are a type of specialized cell junction found exclusively in animal cells. These structures serve as robust, spot-like anchors that physically link two adjacent cells together. Their primary function is to provide strong mechanical adhesion, which is necessary to maintain the integrity of tissues under constant physical stress. Desmosomes act much like rivets, distributing tension and preventing cell layers from being pulled apart.
Defining Desmosomes: Structure and Components
The physical structure of a desmosome is an intricate molecular assembly that spans from one cell’s interior, across the extracellular space, and into the next cell’s interior. The core of the desmosome is made up of transmembrane adhesion proteins, specifically Desmoglein and Desmocollin, which are members of the cadherin family. These proteins extend from the plasma membrane of each cell and interlock in the space between the cells, forming the adhesive bond.
Inside the cell, these transmembrane proteins anchor to a dense, disc-shaped structure called the inner cytoplasmic plaque. This plaque is formed by linker proteins, including Plakoglobin and Plakophilins, which belong to the Armadillo protein family. A large protein called Desmoplakin then connects to these linker proteins, acting as the bridge to the cell’s internal skeleton.
Desmoplakin is responsible for tethering the entire complex to the intermediate filament network within the cell’s cytoplasm. In epithelial cells, these intermediate filaments are typically keratin, while in cardiac muscle they are desmin.
Where Desmosomes Provide Mechanical Strength
This robust anchoring mechanism is concentrated in certain animal tissues that are subject to stretching, shearing, or constant pressure. A prime example is the epithelial layer of the skin, the epidermis, which must withstand external friction and tension without tearing.
Desmosomes are also abundantly found in the lining of the digestive tract, where they maintain cell-to-cell adhesion despite the constant movement and abrasion of food passing through. In the heart muscle, desmosomes are a major component of the intercalated discs that link individual cardiac cells. This anchoring allows the heart muscle cells to contract rhythmically and powerfully without separating from one another under the immense strain of pumping blood.
The integrity provided by these junctions is so significant that genetic mutations affecting desmosomal proteins can lead to diseases where tissues lose their cohesion. For instance, certain heart conditions and blistering skin disorders are directly linked to a failure in the desmosome-intermediate filament complex.
Cell Connection Mechanisms in Plants
Plant cells do not possess desmosomes because their overall structural stability is achieved through a different mechanism involving the cell wall. Plant cells are encased in a rigid cellulose cell wall, which provides the primary mechanical support and structural integrity for the entire organism. This external rigidity means plants do not require the specialized internal anchoring junctions found in animals to resist tensile stress.
Instead of desmosomes, plant cells utilize structures called Plasmodesmata to connect adjacent cells. Plasmodesmata are narrow, membrane-lined channels that pass directly through the thick cell walls, creating cytoplasmic continuity between neighboring cells. This forms a unified network called the symplast, allowing for direct communication and resource sharing.
The function of Plasmodesmata is primarily focused on transport and communication rather than purely mechanical adhesion. They facilitate the movement of various substances, including water, small metabolites, signaling molecules, and even certain proteins, between cells. Within the channel, a narrow tube of the endoplasmic reticulum, known as the desmotubule, runs through the center.