Editing Golgi apparatus (section)

== Function ==

[[File:0314 Golgi Apparatus a en.png|thumb|400px|The Golgi apparatus (salmon pink) in context of the secretory pathway]]

The Golgi apparatus is a major collection and dispatch station of protein products received from the endoplasmic reticulum. Proteins synthesized in the ER are packaged into vesicles, which then fuse with the Golgi apparatus. These cargo proteins are modified and destined for secretion via [[exocytosis]] or for use in the cell.
In this respect, the Golgi can be thought of as similar to a post office: it packages and labels items which it then sends to different parts of the cell or to the [[extracellular space]]. The Golgi apparatus is also involved in [[lipid]] transport and lysosome formation.<ref name="Campbell-1996">{{cite book | first = Neil A | last = Campbell| title = Biology | url = https://archive.org/details/biologycamp00camp | url-access = registration | edition = 4| publisher = Benjamin/Cummings | location = Menlo Park, CA| year = 1996 | pages = [https://archive.org/details/biologycamp00camp/page/122 122], 123| isbn = 978-0-8053-1957-6}}</ref>

The structure and function of the Golgi apparatus are intimately linked. Individual stacks have different assortments of enzymes, allowing for progressive processing of cargo proteins as they travel from the cisternae to the trans Golgi face.<ref name="Alberts-1994"/><ref name="Day-2013"/> Enzymatic reactions within the Golgi stacks occur exclusively near its membrane surfaces, where enzymes are anchored. This feature is in contrast to the ER, which has soluble proteins and enzymes in its [[Lumen (anatomy)|lumen]]. Much of the enzymatic processing is [[post-translational modification]] of proteins. For example, phosphorylation of [[oligosaccharide]]s on lysosomal proteins occurs in the early CGN.<ref name="Alberts-1994"/> ''Cis'' [[cisterna]] are associated with the removal of [[mannose]] residues.<ref name="Alberts-1994"/><ref name="Day-2013"/> Removal of mannose residues and addition of [[N-acetylglucosamine]] occur in medial cisternae.<ref name="Alberts-1994"/> Addition of [[galactose]] and [[sialic acid]] occurs in the ''trans'' cisternae.<ref name="Alberts-1994"/> [[Sulfation]] of [[tyrosine]]s and [[carbohydrate]]s occurs within the TGN.<ref name="Alberts-1994"/> Other general post-translational modifications of proteins include the addition of carbohydrates ([[glycosylation]])<ref name="Flynne-2008">{{cite book|author=William G. Flynne|title=Biotechnology and Bioengineering|url=https://books.google.com/books?id=WEBBP5IYqJQC&pg=PA45|access-date=13 November 2010|year=2008|publisher=Nova Publishers|isbn=978-1-60456-067-1|pages=45–}}</ref> and phosphates ([[phosphorylation]]). Protein modifications may form a [[Signal peptide|signal sequence]] that determines the final destination of the protein. For example, the Golgi apparatus adds a [[mannose-6-phosphate]] label to proteins destined for lysosomes. Another important function of the Golgi apparatus is in the formation of [[proteoglycans]]. Enzymes in the Golgi append proteins to [[glycosaminoglycan]]s, thus creating proteoglycans.<ref name="Prydz-2000">{{cite journal | vauthors = Prydz K, Dalen KT | title = Synthesis and sorting of proteoglycans | journal = Journal of Cell Science | volume = 113 Pt 2 | pages = 193–205 | date = January 2000 | pmid = 10633071 | series = 113 | issue = 2 | doi = 10.1242/jcs.113.2.193 | doi-access = free }}</ref> Glycosaminoglycans are long unbranched [[polysaccharide]] molecules present in the [[extracellular matrix]] of animals.