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How do coated vesicles go to the right place and fuse with the right membrane?

How do coated vesicles go to the right place and fuse with the right membrane?. The “SNARE” hypothesis. SNARE. Vesicle-SNAP-receptors (v-SNAREs) Target-SNAP-receptors (t-SNAREs) SNAP=soluble NSF attachment proteins NSF=N-ethylmaleimide-sensitive factor. Lysosomes. Digestive enzymes

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How do coated vesicles go to the right place and fuse with the right membrane?

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  1. How do coated vesicles go to the right place and fuse with the right membrane? The “SNARE” hypothesis

  2. SNARE • Vesicle-SNAP-receptors (v-SNAREs) • Target-SNAP-receptors (t-SNAREs) • SNAP=soluble NSF attachment proteins • NSF=N-ethylmaleimide-sensitive factor

  3. Lysosomes • Digestive enzymes • Low pH (4-5) • Develop from late endosomes/hydrolases from Golgi • Activated by lowering the pH

  4. Extracellular components • Cell walls • Extracellular matrix • Bone • Cartilage • Connective tissue

  5. Types of molecules in ECM • Structural proteins—strength/flexibility • Collagen • Elastin • Proteoglycans--matrix • Adhesive glycoproteins—stick cells to matrix • Fibronectins • laminins

  6. Collagen--strength

  7. Synthesis--fibroblasts

  8. Elastin--flexibility

  9. Glycosaminoglycans

  10. Proteoglycans—hydrated matrix

  11. Adhesive glycoproteins • Extracellular • Fibronectins • Laminins • Cell surface • Integrins

  12. Fibronectins • Group of adhesive glycoproteins • 2 long linked proteins • Several binding domains

  13. Fibronectin roles • Anchor cells to ECM • Maintain cell shape • Cell movement • Blood clotting

  14. Laminins • Found in basal laminae • Special ECM • Under epithelial cells • Separates them from connective tissue • Role of basal laminae • Support • Permeability barrier • Contain • Type IV collagen • Proteoglycans • laminins

  15. Laminins • Very large proteins • 3 linked peptides • Multiple domains

  16. What binds the cells to the ECM?

  17. Integrins • Groups of transmembrane proteins • Link cytoskeleton to ECM • Fibronectin receptor is best known

  18. Cell-cell interactions Cell-cell adhesion Cell-cell communication

  19. Cell-cell adhesion • Cell adhesion molecules (CAMs) • Lots of them • Involved in many cellular processes • Cadherins • Adhesive glycoproteins

  20. Cell juctions • Adhesive junctions • Strong links • Tight junctions • Prevent leaks between cells • Gap junctions • Forms direct link between cells

  21. Adhesive junctions • Desmosomes • Hemidesmosomes • Adherens junctions • Focal adhesions All contain - intracellular attachment proteins—link to cytoskeleton - transmembrane linker proteins—link the cells

  22. Desmosomes—rivets between cells

  23. Adherens junctions • Belt around cell • Connects to actin, not tonofilaments • Look a lot like desmosomes • Found in • Heart • Epithelial layers • Oftern form belt • Called “focal adhesion” if connects to ECM

  24. Tight junctions

  25. Gap junctions • Direct electrical connection • Formed by connexons • Protein=connexin • Prominent in muscle and nerve—e.g. electrical tissues • Form of cell-cell communication

  26. Cell walls

  27. Plant cell walls • Cellulose (40%) • Branched polysaccharides • Hemicellulose (20%) • Pectins (30%) • Extensins--glycoproteins (10%) • Lignins—woody tissues • Insoluble aromatic alcohols • Cross-link to form wood

  28. Plasmodesmata

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