Endocytosis and exocytosis are both types of bulk transport that move substances in and out of the cell via the use of secretory vesicles. Exocytosis is the process by which materials are moved out of a cell. Endocytosis is the process by which materials are moved into the cell. Endocytosis and exocytosis both require the use of energy in the form of ATP. Types of endocytosis and exocytosis are listed below. A definition and examples of each process are identified.
Process 1, Example of Endocytosis: The Golgi complex creates secretory vesicles around macromolecules within the cytoplasm such as digestive enzymes or hormones. These secretory vesicles fuse with the plasma membrane and are exported from the cell via exocytosis.
Process 2: Phagocytosis is a form of endocytosis. Phagocytosis means “cell eating”. During phagocytosis, a cell’s plasma membrane surrounds a macromolecule. This vesicle then pinches off into the cell to form a food vacuole. The food vacuole then fuses with a lysosome. The hydrolytic enzymes within the lysosome help to digest the contents within the food vacuole. Phagocytosis is a non-specific process.
Process 3, Example of Phagocytosis: Amoebas use phagocytosis in order to obtain energy.
Process 4: Pinocytosis is a form of endocytosis. Like phagocytosis, pinocytosis is also a non-specific process. Pinocytosis means “cell drinking”. During pinocytosis, a cell’s membrane surrounds a fluid. A vacuole that is smaller than a food vacuole of phagocytosis is formed. The solutes within the vacuole then enter the cell.
Process 5: Receptor-mediated endocytosis is a selective form of endocytosis. Receptor-mediated endocytosis uses selective receptor proteins that are located within coated pits of the cell membrane in order to determine what can enter the cell. If the shape of an extracellular molecule does not match the shape of the receptor protein of the coated pit, then that extracellular molecule is not allowed into the cell. If the shape does match, then the coated pit pinches inward to form a coated vesicle. The coated vesicle then fuses with a lysosome so its contents can be digested.
Process 6, Example of receptor-mediated endocytosis: Cholesterol, in the form of low-density lipoproteins (LDLs), is taken into mammal cells via receptor-mediated endocytosis.
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