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Wize University Biology Textbook > The Plasma Membrane

Bulk Transport

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Endocytosis and Exocytosis

A way for molecules to enter or exit the cell without requiring them to pass through the membrane structure. Both require energetic input and utilize the cell membrane.

Exocytosis

Membrane-bound intracellular vesicles merge with the cell membrane to expel its contents into the extracellular space.

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Endocytosis:

Can be thought of as the opposite of exocytosis. Membrane folds into the cell (invaginates) and pinch off to produce membrane-bound vesicles inside the cell containing extracellular components/fluids. There are three main types:



  1. Pinocytosis: fluid endocytosis ("cell drinking")
  2. Most cells can do this.
  3. Phagocytosis: solid endocytosis ("cell eating")
  4. Cell engulfs bacteria, other cell debris from tissue death, etc.
  5. Pseudopodia ("sham feet") are created to surround material;
  6. Usually specialized cells such as macrophages/other immune cells.
  7. Receptor-mediated endocytosis: specific uptake triggered by receptor binding
  8. Clathrin-dependent
  9. Formation of a clathrin-coated vesicle Example: cholesterol binds to LDL receptor in liver and clathrin is recruited in cytoplasm and coats the vesicles from the inside.
  10. Potocytosis: clathrin-independent
  11. Formation of tiny vesicles called caveolae that deliver their contents to cytosol.

Practice: Phagocytosis

Which of the following statement(s) are false regarding phagocytosis?

Practice: Pinocytosis

Pinocytosis: