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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