OpenStax Biology 2e
Cells can also communicate with each other via direct contact, or intercellular junctions. There are differences in the ways that plant and animal and fungal cells communicate. Plasmodesmata are junctions between plant cells; whereas, animal cell contacts include tight junctions, gap junctions, and desmosomes.
In general, long stretches of the plasma membranes of neighboring plant cells cannot touch one another because the cell wall that surrounds each cell separates them. How then, can a plant transfer water and other soil nutrients from its roots, through its stems, and to its leaves? Such transport uses the vascular tissues (xylem and phloem) primarily. There also exist structural modifications, which we call plasmodesmata (singular = plasmodesma). Numerous channels that pass between adjacent plant cells’ cell walls connect their cytoplasm, and enable transport of materials from cell to cell, and thus throughout the plant.
A tight junction is a watertight seal between two adjacent animal cells. Proteins (predominantly two proteins called claudins and occludins) tightly hold the cells against each other.
This tight adherence prevents materials from leaking between the cells; tight junctions are typically found in epithelial tissues that line internal organs and cavities, and comprise most of the skin. For example, the tight junctions of the epithelial cells lining your urinary bladder prevent urine from leaking out into the extracellular space.
Also only in animal cells are desmosomes, which act like spot welds between adjacent epithelial cells. Cadherins, short proteins in the plasma membrane connect to intermediate filaments to create desmosomes. The cadherins connect two adjacent cells and maintain the cells in a sheet-like formation in organs and tissues that stretch, like the skin, heart, and muscles.
Gap junctions in animal cells are like plasmodesmata in plant cells in that they are channels between adjacent cells that allow for transporting ions, nutrients, and other substances that enable cells to communicate. Structurally, however, gap junctions and plasmodesmata differ.
Gap junctions develop when a set of six proteins (connexins) in the plasma membrane arrange themselves in an elongated donut-like configuration – a connexon. When the connexon’s pores (“doughnut holes”) in adjacent animal cells align, a channel between the two cells forms. Gap junctions are particularly important in cardiac muscle. The electrical signal for the muscle to contract passes efficiently through gap junctions, allowing the heart muscle cells to contract in tandem.– What are multi-protein junctional complexes whose general function is to prevent leakage of transported solutes and water and seals the para-cellular pathway. ?
– What are a specialized inter-cellular connection between a multitude of animal cell-types. They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells?
– What are protein complexes that occur at cell–cell junctions in epithelial and endothelial tissues, usually more basal than tight junctions, and are defined as a cell junctions whose cytoplasmic face is linked to the actin cytoskeleton.?
Desmosomes are major cell-cell junctions that are particularly abundant in epidermal cells and cardiomyocytes. Arrhythmogenic Right Ventricular Dysplasia may be caused by genetic defects of the structure of myocardial desmosomes. Desmosomes are multiprotein complexes that form intercellular contacts on the surface of heart muscle cells. Mutations in many proteins that comprise desmosomes can have harmful effects on cardiomyocyte function. Defective desmosomes cannot sustain the constant mechanical stress inherent in contracting cardiomyocytes, resulting in cardiomyocyte detachment and the consequent impairment of mechanical and electrical cell junctions.
Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e