Tight junction: Difference between revisions
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Tight junctions, or otherwise known as zona occludens, are junctional structures between the plasma membrane of two adjacent cells and control paracellular movement of molecules through epithelial layers. They are easily seen in intestinal epithelial cells and are also abundant in the ducts and cavities of glands, such as the liver pancreas and urinary bladder. Tight junctions form a continuous belt around the apical ends of the lateral surfaces of each cell, preventing the movement of fluids, [[Ions|ions]] and molecules between cells. Tight junctions also block the lateral movement of larger molecules like lipids and proteins within the membrane. The different concentrations of different kinds of integral proteins in the plasma membrane can then be maintained<ref>Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin, Gregory Paul Bertoni (2009), The World of the Cell, Pearson International Edition, 7th Edition, P.489</ref>. | Tight junctions, or otherwise known as [[zona occludens|zona occludens]], are junctional structures between the [[plasma membrane|plasma membrane]] of two adjacent [[cells|cells]] and control paracellular movement of [[molecules|molecules]] through [[Epithelial_cell|epithelial]] layers. They are easily seen in intestinal epithelial cells and are also abundant in the ducts and cavities of glands, such as the [[liver|liver]], [[pancreas|pancreas]] and urinary bladder. Tight junctions form a continuous belt around the [[Apical_membrane|apical]] ends of the lateral surfaces of each cell, preventing the movement of fluids, [[Ions|ions]] and molecules between cells. Tight junctions also block the lateral movement of larger molecules like [[lipids|lipids]] and [[proteins|proteins]] within the membrane. The different concentrations of different kinds of integral proteins in the [[plasma membrane|plasma membrane]] can then be maintained <ref>Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin, Gregory Paul Bertoni (2009), The World of the Cell, Pearson International Edition, 7th Edition, P.489</ref><ref>Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin, Gregory Paul Bertoni (2009), The World of the Cell, Pearson International Edition, 7th Edition, P.488</ref>. | ||
Tight junctions consist of three major proteins. [[Occludin|Occludin]] is a 65 kDa tetra-spanning protein with two short extracellular domains and a highly extended [[C terminal|C terminus]]. Claudin family of proteins are the major proteins in tight junctions and are 23 kDa tetra-spanning proteins with two short extracellular domains. Both proteins have cytosolic C and T terminals and there are over 20 Claudin proteins. Junctional adhesion molecule is also involved in the formation of tight junctions. It has one membrance span and to immunoglobulin folds in its extracellular domain. Together these proteins for a "zipper" across the cleft between two adjacent cells. | |||
The composition of the Claudin proteins determines whether the junction is tight or leaky. The introduction of Claudin 2 into the junction produces a leaky junction. Heterodimers that include Claudin 2 do not fit tightly together and, therefore, allow molecules to pass through. | The composition of the Claudin proteins determines whether the junction is tight or leaky. The introduction of Claudin 2 into the junction produces a leaky junction. Heterodimers that include Claudin 2 do not fit tightly together and, therefore, allow molecules to pass through. | ||
= References = | === References === | ||
<references /> | <references /> | ||
Revision as of 18:03, 23 October 2012
Tight junctions, or otherwise known as zona occludens, are junctional structures between the plasma membrane of two adjacent cells and control paracellular movement of molecules through epithelial layers. They are easily seen in intestinal epithelial cells and are also abundant in the ducts and cavities of glands, such as the liver, pancreas and urinary bladder. Tight junctions form a continuous belt around the apical ends of the lateral surfaces of each cell, preventing the movement of fluids, ions and molecules between cells. Tight junctions also block the lateral movement of larger molecules like lipids and proteins within the membrane. The different concentrations of different kinds of integral proteins in the plasma membrane can then be maintained [1][2].
Tight junctions consist of three major proteins. Occludin is a 65 kDa tetra-spanning protein with two short extracellular domains and a highly extended C terminus. Claudin family of proteins are the major proteins in tight junctions and are 23 kDa tetra-spanning proteins with two short extracellular domains. Both proteins have cytosolic C and T terminals and there are over 20 Claudin proteins. Junctional adhesion molecule is also involved in the formation of tight junctions. It has one membrance span and to immunoglobulin folds in its extracellular domain. Together these proteins for a "zipper" across the cleft between two adjacent cells.
The composition of the Claudin proteins determines whether the junction is tight or leaky. The introduction of Claudin 2 into the junction produces a leaky junction. Heterodimers that include Claudin 2 do not fit tightly together and, therefore, allow molecules to pass through.
References
- ↑ Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin, Gregory Paul Bertoni (2009), The World of the Cell, Pearson International Edition, 7th Edition, P.489
- ↑ Wayne M. Becker, Lewis J. Kleinsmith, Jeff Hardin, Gregory Paul Bertoni (2009), The World of the Cell, Pearson International Edition, 7th Edition, P.488