Wize AP Biology Textbook > The Plasma Membrane
Bulk Transport
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Find My CourseEndocytosis 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.
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:
- Pinocytosis: fluid endocytosis ("cell drinking")
- Most cells can do this.
- Phagocytosis: solid endocytosis ("cell eating")
- Cell engulfs bacteria, other cell debris from tissue death, etc.
- Pseudopodia ("sham feet") are created to surround material;
- Usually specialized cells such as macrophages/other immune cells.
- Receptor-mediated endocytosis: specific uptake triggered by receptor binding
- Clathrin-dependent
- 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.
- Potocytosis: clathrin-independent
- 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: