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Exocytosis and its counterpart, endocytosis, are used by all cells because most chemical substances important to them are large polar molecules that cannot pass through the hydrophobic portion of the cell membrane by passive means. Exocytosis is the process by which a large amount of molecules are released; thus it is a form of bulk transport.
Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested materials. Endocytosis includes pinocytosis (cell drinking) and phagocytosis (cell eating). It is a form of ...
Exocytosis (L) and Endocytosis (R) Exocytosis is when a cell directs the contents of secretory vesicles out of the cell membrane. The vesicles fuse with the cell membrane and their content, usually protein, is released out of the cell. There are two types of exocytosis: Constitutive secretion and Regulated secretion.
In phagocytosis, involving the destruction of pathogens, the pathogens are surrounded and then engulfed through endocytosis. The vacuole then forms and closes around the pathogens. In exocytosis, the lysosome and vacuole fuse together which allows enzymes to destroy pathogens. Debris from the pathogens is then released from the cell.
Exocytosis is the process by which a large amount of molecules are released; thus it is a form of bulk transport. Exocytosis occurs via secretory portals at the cell plasma membrane called porosomes. Porosomes are permanent cup-shaped lipoprotein structures at the cell plasma membrane, where secretory vesicles transiently dock and fuse to ...
However, receptor-mediated endocytosis is also actively implicated in transducing signals from the cell periphery to the nucleus. This became apparent when it was found that the association and formation of specific signaling complexes via clathrin-mediated endocytosis is required for the effective signaling of hormones (e.g. EGF).
The cytopharynx in this way acts much like a straw that sucks macromolecules to the posterior end of the cell. The passage of macromolecules from the entrance of the cytostome to the posterior end of the cytopharynx takes at least 2 minutes. The cytostome is the main site of endocytosis in Trypanosoma cruzi epimastigotes. [6]
Receptor-mediated endocytosis is a form of pinocytosis where a cell takes in specific molecules or solutes. Proteins with receptor sites are located on the plasma membrane, binding to specific solutes. The receptor proteins that are attached to the specific solutes go inside coated pits, forming a vesicle.