Endocytosis

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Endocytosis is the process by which cells absorb molecules (such as proteins) by engulfing them. It is used by all cells of the body because most substances important to them are large polar molecules that cannot pass through the hydrophobic plasma or cell membrane. The process opposite to endocytosis is exocytosis. Endocytosis pathways could be subdivided into four categories: namely, clathrin-mediated endocytosis, caveolae, macropinocytosis, and phagocytosis. Clathrin-mediated endocytosis is mediated by small (approx. 100 nm in diameter) vesicles that have a morphologically characteristic crystalline coat made up of a complex of proteins that mainly associated with the cytosolic protein clathrin. Clathrin-coated vesicles (CCVs) are found in virtually all cells and from domains of the plasma membrane termed clathrin-coated pits.