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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.[1] 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.

The process of regulated exocytosis. Secretory vesicles containing molecules, shown as purple orbs, being secreted, forming vesicles in the cytoplasm and moving towards the cell membrane, before the vesicle fuses with the membrane, releasing its contents into the extracellular fluids. The arrows show the secretory vesicles directional movement, as well as labelling key components, such as the cytoplasm, the cell membrane and the extracellular fluid. Made in biorender.com

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.[2] 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.[3][4] 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.[5] 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.[6] This is one of tree processes in which exocytosis can be performed, where the two others are constitutive exocytosis[7][8] and outer-membrane vesicle mediated exocytosis.[9]

  1. ^ Wu, Ling-Gang; Hamid, Edaeni; Shin, Wonchul; Chiang, Hsueh-Cheng (2014). "Exocytosis and endocytosis: modes, functions, and coupling mechanisms". Annual Review of Physiology. 76: 301–331. doi:10.1146/annurev-physiol-021113-170305. PMC 4880020. PMID 24274740.
  2. ^ Viotti, Corrado (2016). "ER to Golgi-Dependent Protein Secretion: The Conventional Pathway". Unconventional Protein Secretion. Methods in Molecular Biology. Vol. 1459. pp. 3–29. doi:10.1007/978-1-4939-3804-9_1. ISBN 978-1-4939-3802-5. PMID 27665548.
  3. ^ Schweizer, Felix E; Ryan, Timothy A (June 2006). "The synaptic vesicle: cycle of exocytosis and endocytosis". Current Opinion in Neurobiology. 16 (3): 298–304. doi:10.1016/j.conb.2006.05.006. PMID 16707259.
  4. ^ Bonifacino, Juan S; Glick, Benjamin S (January 2004). "The Mechanisms of Vesicle Budding and Fusion". Cell. 116 (2): 153–166. doi:10.1016/S0092-8674(03)01079-1. PMID 14744428.
  5. ^ Cite error: The named reference Jahn-2006 was invoked but never defined (see the help page).
  6. ^ Cocucci, Emanuele; Meldolesi, Jacopo (2013). "Nonsecretory, Regulated Exocytosis: A Multifarious Mechanism Employed by Cells to Carry Out a Variety of Functions". Madame Curie Bioscience Database [Internet]. Landes Bioscience.
  7. ^ Litwack, Gerald (2018). "Membrane Transport". Human Biochemistry. pp. 553–589. doi:10.1016/B978-0-12-383864-3.00018-1. ISBN 978-0-12-383864-3.
  8. ^ Cite error: The named reference Tran-2017 was invoked but never defined (see the help page).
  9. ^ Yáñez-Mó, María; Siljander, Pia R.-M.; Andreu, Zoraida; Zavec, Apolonija Bedina; Borràs, Francesc E.; Buzas, Edit I.; Buzas, Krisztina; Casal, Enriqueta; Cappello, Francesco; Carvalho, Joana; Colás, Eva; Cordeiro-da Silva, Anabela; Fais, Stefano; Falcon-Perez, Juan M.; Ghobrial, Irene M. (2015). "Biological properties of extracellular vesicles and their physiological functions". Journal of Extracellular Vesicles. 4: 27066. doi:10.3402/jev.v4.27066. PMC 4433489. PMID 25979354.

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