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Lecture

BIOL 2021 Lecture Notes - Tight Junction, Transcellular Transport, Cell Adhesion


Department
Biology
Course Code
BIOL 2021
Professor
Julie Clark

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BIOL 2021- May 12 2009
CHAPTER 19: CELL JUNCTIONS, ADHESION AND EXTRACELLULAR MATRIX
Architecture
Cell junctions
Cell adhesion
Extracellular matrix=ECM
Proteins and polysaccharides secreted by cells
Figure 19.1:architecture of animal tissue
Building strategies
1) Few cells in ECM
Used in connective tissue; matrix of fibrous polymers causes stress
2) Cell-cell adhesion and cytoskeleton
- Cytoskeleton is prominent
Used in epithelial cells on basal lamina (thin ECM)
- Stress carried by cytoskeleton
CELL JUNCTIONS
Figure 19.2: classification of junctions

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1) Anchoring junction
- Cell to cell adhesion
- Cell-matrix adhesion
- Purpose is to transmit stress
- Tethered to cytoskeleton
2) Occluding junctions
- Seals up gaps between epithelial cells
3) Channel forming junction
- Links cytoplasm of neighbouring cells
4) Signal relaying junction
- Found in nerve cells
- Relays signal between cells
*** TABLE 19-1: CLASSIFICAION OF CELL JUNCTIONS
OCCULUDING JUNCTIONS
Figure: tight junctions in transcellular transport
- Trans cellular transport

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- Tight junctions in epithelial cells
- 60% of all cell types= epithelium
- In epithelium cells, cells are polarized=
Basal side: anchored
Apical side: free
- Tight junctions keep transport proteins segregated
Sodium can diffuse across tight junctions
Figure: a) sealing strands in tight junctions b) claudins in tight junctions
- Structure in tight junction
Row of sealing strands
Figure: TEM of tight junctions
- Proteins= claudin, adhesion protein
CHANNEL FORMING JUNCTION
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