Exocytosis and Endocytosis Exocytosis and Endocytosis A Closer Look at Cell Membranes . Aim: How do large particles enter and exit cells? . Do Now: Name some molecules/materials that enter and exit the cell. How would you describe the cell membrane that allows passage of these materials? Exocytosis and Endocytosis Exocytosis and Endocytosis . Exocytosis (out of the cell) • The fusion of a vesicle with the cell membrane, releasing its contents to the surroundings . Endocytosis (into the cell) • The formation of a vesicle from cell membrane, enclosing materials near the cell surface and bringing them into the cell Exocytosis and Endocytosis Endocytosis . Phagocytosis – solid . Pinocytosis – liquid (general) Endocytosis: . Uptake of substances . Transport of protein or lipid components of compartments . Metabolic or division signaling . Defense to microorganisms Endocytosis . Clathrin-coated vesicles . Non-clathrin coated vesicles . Macropinocytosis . Potocytosis Exocytosis and Endocytosis Endocytosis Required: . signal . membrane receptor (Fc receptor for Ab) . formation of pseudopodium . cortical actin network The formed vesicle: phagosome (hetero-; auto-) Endocytosis . Clathrin-coated vesicles . Non-clathrin coated vesicles . Macropinocytosis . Potocytosis Endocytosis and Exocytosis Examples Three Pathways of Endocytosis . Bulk-phase endocytosis • Extracellular fluid is captured in a vesicle and brought into the cell; the reverse of exocytosis . Receptor-mediated endocytosis • Specific molecules bind to surface receptors, which are then enclosed in an endocytic vesicle . Phagocytosis • Pseudopods engulf target particle and merge as a vesicle, which fuses with a lysosome in the cell Phagocytosis (“engulfment”) Exocytosis and Endocytosis Membrane Cycling . Exocytosis and endocytosis continually replace and withdraw patches of the plasma membrane . New membrane proteins and lipids are made in the ER, modified in Golgi bodies, and form vesicles that fuse with plasma membrane Exocytic Vesicle 5.5 Key Concepts: Membrane Trafficking . Large packets of substances and engulfed cells move across the plasma membrane by processes of endocytosis and exocytosis . Membrane lipids and proteins move to and from the plasma membrane during these processes Exocytosis and Endocytosis Macropinocytosis . Ruffling of the surface membrane forms inclusions . These „vacuoles” have no membrane . Size 0.2-5 mm - the mass/surface ratio is very good . Significance: . Liquide-phase pinocytosis . Taking probes from the . environment . – antigene recognition . in macrophages Exocytosis and Endocytosis Exocytosis in TEM THE END.