1. The “SNARE” hypothesis
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

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

6. Extracellular components
Cell walls
Extracellular matrix
Bone
Cartilage
Connective tissue

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

8. Collagen--strength

9. Synthesis--fibroblasts

10. Elastin--flexibility

11. Glycosaminoglycans

12. Proteoglycans—hydrated matrix

13. Adhesive glycoproteins
Extracellular
Fibronectins
Laminins
Cell surface
Integrins

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

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

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

18. Laminins
Very large proteins
3 linked peptides
Multiple domains

20. What binds the cells to the ECM?

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

23. Cell-cell interactions
Cell-cell adhesion
Cell-cell communication

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

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

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

29. Desmosomes—rivets between cells

31. 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

32. Tight junctions

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

38. Cell walls

39. 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

41. Plasmodesmata