Our body is made up of many cells and this cells are linked with each other and have different functions, so today we are going to discuss something about cell junctions and their functions. Our main objective is to study tight junction,gap junction and desmosomes.
Tight junction,gap junction and desmosomes.
Difference between tight junction,gap junction and desmosomes.
Tight junction: The role of tight junctions in transcellular transport. Transport proteins are confined to different regions of the plasma membrane in epithelial cells of the small intestine. This segregation permits a vectorial transfer of nutrients across the epithelium
The tight junctions between epithelial cells are thought to have both of these roles. First, they function as barriers to the diffusion of some membrane proteins (and lipids) between apical and basolateral domains of the plasma membrane. Mixing of such proteins and lipids occurs if tight junctions are dirsupted, for example, by removing the extracellular Ca2+ that is required for tight junction integrity. Second, tight junctions seal neighboring cells together so that, if a low-molecular-weight tracer is added to one side of an epithelium, it will generally not pass beyond the tight junction seal is not absolute, however. Although all tight junctions are impermeable to macromolecules, their permeability to small molecules varies greatly in different epithelia. Tight junctions in the epithelium lining the small intestine, for example, are 10,000 times more permeable to inorganic ions, such as Na+, than the tight junctions in the epithelium lining the urinary bladder. These differences reflect differences in tight junction proteins that form the junctions.
Gap junction: Gap junctions are communicating junctions composed of clusters of connexons that allow molecules smaller than about 1000 daltons to pass directly from the inside of one cell to the inside of the next. Cells connected by gap junctions share many of their inorganic ions and other small molecules and are therefore chemically and electrically coupled. Gap junctions are important in coordinating the activities of electrically active cells, and they have a coordinating role in other groups of cells as well. Plasmodesmata are the only intercellular junctions in plants. Although their structure is entirely different, and they can sometimes transport informational macromolecules, in general, they function like gap junctions.
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Refrences: http://www.ncbi.nlm.nih.gov › … › Both