1. Copyright © 2005 Pearson Prentice Hall, Inc. Intracellular Compartments and Transport Membrane Enclosed Organelles Protein Sorting Vesicular Transport Secretory Pathways Endocytic Pathways http://aimediaserver.com/studiodaily/videoplayer/?src=harvard/harvard.swf&width=640&height=520

2. Copyright © 2005 Pearson Prentice Hall, Inc. Intracellular Compartments and Transport: Vesicular Transport Function: carry soluble proteins & membrane between compartments Budding: driven by assembly of a protein coat Docking: specificity depends on SNARES

3. Copyright © 2005 Pearson Prentice Hall, Inc. VESICULAR TRANSPORT Vesicles bud off a compartment Transport between compartments –Secretory Pathway: Golgi to plasma membrane –Endocytic Pathway: plasma membrane to endosome to lysosome

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5. VESICULAR TRANSPORT 1.Vesicles bud off a compartment 2.Transport between compartments Secretory Pathway: Golgi to plasma membrane Endocytic Pathway: plasma membrane to endosome to lysosome

6. Copyright © 2005 Pearson Prentice Hall, Inc. Vesicle Budding Protein coat assembly –on cytosolic surface –COP- coated ER to Golgi Within Golgi –Clathrin coated Clathrin coated pit Dynamin protein : constriction, binds GTP Adaptin proteins: anchor clathrin, cargo receptors Cargo receptor : bind transport signals

7. Copyright © 2005 Pearson Prentice Hall, Inc. Clathrin: Clathrin Coated Pit => Clatherin Coated Vesicle

8. Copyright © 2005 Pearson Prentice Hall, Inc. Clathrin coated pit Dynamin protein : constriction, binds GTP Adaptin proteins: anchor clathrin, cargo receptors Cargo receptor : bind transport signals Vesicle Budding: Clathrin

9. Copyright © 2005 Pearson Prentice Hall, Inc. Vesicle Docking Organelle Recognition v-SNARE t-SNARE Membrane Fusion –Water removed: enzyme complex –Intertwining of SNAREs

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11. Endocytic Pathways 1.Phagocytosis: Specialized Phagocytic Cells Ingest Large Particles 2.Pinocytosis: Take up Fluids and Macomolecdules 3.Receptor Mediated Endocytosis: Forms A Specific Route into Animal Cells 4.Endsomes: Sorting Endocytosed Macromolecules 5.Lysosomes: Principal Site of Intracellular Digestion

12. Copyright © 2005 Pearson Prentice Hall, Inc. Endocytic Pathway: Phagocytosis, Pinocytosis Phagocytosis : phagocytic cells (macrophages) –Bacteria, dead or damaged cells, deris –Pseudopods form phagosome –Phagosomes fuse with lysosomes YB bacteria : interfere with fusion –Recognition molecules : phagocytic receptors Opsonised bacteria

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14. Endocytic Pathway: Pinocytosis –Fluid and small particles –By clathrin –coated pits –Fluid intake balanced by fluid exocytosis

15. Copyright © 2005 Pearson Prentice Hall, Inc. Receptor Mediated Endocytosis: Cholesterol Uptake Cholesterol transported as LDL Endocytosed via receptors for LDL LDL-receptor complex dissociated in endosomes –Receptor recycled to membrane –LDL to lysosome Protein –cholesterol dissociated Cholesterol released to cytosol Genetic condition: defective LDL receptor

16. Copyright © 2005 Pearson Prentice Hall, Inc. Receptor Mediated Endocytosis: Cholesterol Uptake

17. Copyright © 2005 Pearson Prentice Hall, Inc. Fate of Receptors in Endosomes Recycled Degraded Transcytosed

18. Copyright © 2005 Pearson Prentice Hall, Inc. Lysosomes Sacs of hydrolytic enzymes pH ~ 5 : optimal activity of enzymes Enzymes: tagged with mannose-6-P in ER Unique membrane –ATP proton pump –Transport proteins –Membrane proteins glycosylated

19. Copyright © 2005 Pearson Prentice Hall, Inc. Protein Glycosylation

20. Copyright © 2005 Pearson Prentice Hall, Inc. Secretory Pathways Covalent Modification in ER ER Exit Controlled to Ensure Protein Quality Further Modification & Sorting in Golgi Released from Cell by Exocytosis

21. Copyright © 2005 Pearson Prentice Hall, Inc. Secretory Pathways Constitutive Regulated