- Created by: Huzaima1
- Created on: 03-01-19 14:23
Tight Junctions and Gap Junctions
- Tight junctions prevent movement of substances
- Formed by the fusion of integral proteins of adjacent cells
- prevent anything passing through the extra cellular space between them. E.g. cells lining the digestive tract.
- Tight junctions bar the movement of dissolved materials through the space between epithelial cells.
- There is no intercellular space where there is a tight junction.
- Long rows of tight junction proteins form a complex meshwork seen at the bottom of the freeze etched image
- Gap junctions allow movement of substances
- The adjacent cells are connected by hollow cylinders called connexons made of trans membrane proteins. Found in electrically excitable tissues for synchronization e.g. heart and smooth muscle
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Adherens junctions, Desmosomes and Hemidesmosomes:
Desmosomes and Hemidesmosomes:
- These are anchoring junctions held together by linker protein filaments called cadherins or integrins extending from button like thickenings called plaques.
- Distributes tension and prevents tearing.
- e.g. skin and heart muscle
- Plaque which attaches to membrane proteins and the microfilaments of the cytoskeleton
- Often form adhesion belts.
- Resist separation in contractile activities such as peristalsis
- Adhering junctions maintain cellular position
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Cell to Cell junction examples
- Mechanical coupling:
- There is a small gap (0.02 mm) between the membranes of adjacent cells which is filled with connective tissue.
- This firmly binds two adjacent cells together
- Cells are bound together more strongly at certain points called desmosomes.
- Electrical coupling:
- The longitudinal segments contain specialised regions where the membrane of the adjacent cells come very close together.
- In the nexus (gap junction) regular arrays of proteins called connexinsare found
- These form large channels which allow the passage of ions and other small molecules between one cell and another.
- Intercalated discs have two important roles
- They act to firmly bind adjacent cells together (mechanical coupling) but also to allow electrical coupling between adjacent cells
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