Exocytosis

Exocytosis is a term for the active transport process that transports large molecules from cell to the extracellular area. Hormones, proteins and neurotransmitters are examples of large molecules that can be transported out of the cell. Exocytosis is a crucial transport mechanism that enables polar molecules to flow through the cell membranes’ hydrophobic lipid bilayer. The transport process is essential to hormone secretion, immune response and neurotransmission.

Both prokaryotes and eukaryotes undergo exocytosis. Prokaryotes secrete molecules and cellular waste through translocons that are localized to the cell membrane. In addition, they secrete molecules to other cells through specialized organs. Eukaryotes rely on multiple cellular processes to perform the exocytosis process. Eukaryotes have several organelles and a nucleus in the cytoplasm that are connected through multiple transport routes, that is formally known as the secretory pathway. This is a complex pathway with multiple processes, including the exclusion of molecules to the extracellular area. This happens where secretory vesicles transport and fuse with the plasma membrane of the cell to release their contents to the extracellular area.

Different molecules will carry different signal sequences. Proteins carry signal sequences at their N-Terminus, which guides them through the secretory pathway. When reaching the plasma membrane, the vesicles bind to porosomes that are embedded in the membrane. This is a process helped by SNARE proteins (Soluble NSF attachment protein receptors) in regulated exocytosis. This is one of tree processes in which exocytosis can be performed, where the two others are constitutive exocytosis and outer-membrane vesicle mediated exocytosis.