Endocytosis facts for kids

Kids Encyclopedia Facts

Endocytosis is a process whereby cells absorb material (molecules or other cells) from outside by engulfing it with their cell membranes. It is used by cells (especially protists) because most substances important to them are polar and consist of big molecules, and thus cannot pass through the highly hydrophobic plasma membrane. Endocytosis is the opposite of exocytosis, and always involves the formation of a vesicle from part of the cell membrane.

There are three types of endocytosis:

  • Phagocytosis (literally, cell-eating) is the process by which cells ingest large objects, such as prey cells or large chunks of dead organic matter. The membrane folds around the material, and vesicles are sealed off into large vacuoles. Lysosomes then merge with the vacuoles, turning them into a digestive chamber. The products of the digestion are then released into the cytosol. Macrophages are cells of the immune system that specialize in the destruction of antigens (bacteria, viruses and other foreign particles) by phagocytosis.
  • Pinocytosis (literally, cell-drinking) is the invagination of the cell membrane to form a pocket filled with extracellular fluid (and molecules within it). The pocket then pinches off to form a vesicle, and the vesicle ruptures to release its contents into the cytosol.
  • Receptor-mediated endocytosis is similar to pinocytosis, except it is prompted by the binding of a large extracellular molecule - such as a protein - to a receptor on the cell membrane. These receptors are often associated with the cytosolic protein clathrin, which is coating the membrane, forming a pit. When the receptors bind their target molecules, the pit deepens until a clathrin-coated vesicle is released into the cytosol.

Endocytosis Facts for Kids. Kiddle Encyclopedia.