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Animation: Exocytosis and Endocytosis

by Pearson
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Endocytosis is the movement of materials into a cell via vesicles that form from the plasma membrane. Exocytosis is the movement of materials out of a cell by the fusion of vesicles with the plasma membrane. These processes enable patches of membrane to flow back and forth between the interior of the cell and the plasma membrane, reminding us that a cell is a dynamic structure. Exocytosis is the movement of vesicles in the cell to the plasma membrane, where they fuse with the membrane and release their contents into the surrounding fluid. This process occurs predominantly in secretory cells, such as mucus-producing cells or pancreatic cells that secrete enzymes into the digestive tract. In endocytosis, the plasma membrane invaginates, or pinches in, forming a vesicle that moves the enclosed materials inside the cell. There are three types of endocytosis, each involving its own specific cell machinery. In phagocytosis, or cellular eating, the cell engulfs debris, bacteria, or other particles by extending pseudopodia around the material. Invagination produces a food vacuole. The material inside the vacuole will be digested after the food vacuole fuses with a lysosome containing hydrolytic enzymes. Phagocytosis occurs in amoebas and in immune cells such as macrophages and neutrophils in mammals. In pinocytosis, or cellular drinking, the cell engulfs extracellular fluid, including molecules such as sugars and proteins. These materials enter the cell inside a vesicle. Epithelial cells in capillaries use pinocytosis to engulf the liquid portion of blood at the capillary surface. The resulting vesicles travel across the capillary cells and release their contents to surrounding tissues, while blood cells remain in the blood. Unlike phagocytosis and pinocytosis, receptor-mediated endocytosis is very specific. It is triggered when membrane receptors bind to specific external molecules, such as protein-cholesterol complexes or proteins bound to iron. Membrane vesicles pinch off, and the external receptor and its cargo are brought into the cell.
Endocytosis is the movement of materials into a cell via vesicles that form from the plasma membrane. Exocytosis is the movement of materials out of a cell by the fusion of vesicles with the plasma membrane. These processes enable patches of membrane to flow back and forth between the interior of the cell and the plasma membrane, reminding us that a cell is a dynamic structure. Exocytosis is the movement of vesicles in the cell to the plasma membrane, where they fuse with the membrane and release their contents into the surrounding fluid. This process occurs predominantly in secretory cells, such as mucus-producing cells or pancreatic cells that secrete enzymes into the digestive tract. In endocytosis, the plasma membrane invaginates, or pinches in, forming a vesicle that moves the enclosed materials inside the cell. There are three types of endocytosis, each involving its own specific cell machinery. In phagocytosis, or cellular eating, the cell engulfs debris, bacteria, or other particles by extending pseudopodia around the material. Invagination produces a food vacuole. The material inside the vacuole will be digested after the food vacuole fuses with a lysosome containing hydrolytic enzymes. Phagocytosis occurs in amoebas and in immune cells such as macrophages and neutrophils in mammals. In pinocytosis, or cellular drinking, the cell engulfs extracellular fluid, including molecules such as sugars and proteins. These materials enter the cell inside a vesicle. Epithelial cells in capillaries use pinocytosis to engulf the liquid portion of blood at the capillary surface. The resulting vesicles travel across the capillary cells and release their contents to surrounding tissues, while blood cells remain in the blood. Unlike phagocytosis and pinocytosis, receptor-mediated endocytosis is very specific. It is triggered when membrane receptors bind to specific external molecules, such as protein-cholesterol complexes or proteins bound to iron. Membrane vesicles pinch off, and the external receptor and its cargo are brought into the cell.