Tight junctions are found only in a specific area of epithelial cells. Very important for multi-cellular organisms, tight junctions are often characterized by fusion adjacent of the cell membrane. These junctions perform various tasks within membranes. The main process of communication carried out in the cell membrane via different functions including sealing the intercellular space in the endothelial cell layers and epithelial cells. This function alone in cell membrane also prevents free paracellular passage of substances. Tight junctions often ensure the polarity of epithelial cells within the cell membrane. They form a boundary between the apical domain and basolateral domain. With this process, the protein and lipid in the apical domain and basolateral domain defuse. Tight junctions also rely on the molecular shape. The water-soluble and ions also effect these junctions. Their entire process and functions always remain parallel. Tight junctions, which are also important for communication among cells, always hold tight membrane cells in an effort to make boundaries. Aggregation of claudin and occluding proteins are essential part of tight junctions as well.
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Gap junctions are widespread in terms of distribution and they basically provide cells with the means to communicate. They transport ions and small molecules. This functional transport within cell membranes allow chemical and electrical coupling of adjacent cells. This function alone is very important for the human heart and also muscles. The chemical and transport coupling action also allows for regular embryogenesis. The smooth muscle is also called nexus in gap junction. Basically gap junctions are made of integral membrane proteins called connexins. You often find approximately 2nm gap between adjacent cells especially in gap junctions.
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