Golgi Apparatus


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Related to Golgi Apparatus: endoplasmic reticulum, nucleus, Lysosomes, Plastids

Golgi apparatus

An organelle, named after the Italian histologist Camillo Golgi, found in all eukaryotic cells but absent from prokaryotes such as bacteria. It consists of flattened membrane-bounded compartments known as cisternae. In most cells, the Golgi cisternae are organized into stacks. Different cell types contain from one to several thousand Golgi stacks. The Golgi apparatus sorts newly synthesized proteins for delivery to various destinations, and modifies the oligosaccharide chains found on glycoproteins and glycolipids. See Cell organization

The Golgi apparatus acts at an intermediate stage in the secretory pathway. A subset of the proteins synthesized by the cell are inserted into the endoplasmic reticulum. Most such proteins are then delivered to the Golgi apparatus by means of coat protein II (COPII) transport vesicles, which form at endoplasmic reticulum exit sites. Newly synthesized proteins traverse the Golgi stack until they reach the trans-most Golgi compartment, which is termed the trans-Golgi network to connote its extensive tubulation. The trans-Golgi network sorts the proteins into several types of vesicles. Clathrin-coated vesicles carry certain proteins to lysosomes. Other proteins are packaged into secretory vesicles for immediate delivery to the cell surface. Still other proteins are packaged into secretory granules, which undergo regulated secretion in response to specific signals. This sorting function of the Golgi apparatus allows the various organelles to grow while maintaining their distinct identities. See Cell membranes, Endoplasmic reticulum, Lysosome

The best understood of the processing reactions carried out by the Golgi apparatus is the remodeling of oligosaccharides (chains of six-carbon sugars) that are attached to glycoproteins. During insertion of a newly synthesized protein into the endoplasmic reticulum, one or more copies of a 14-sugar oligosaccharide may be attached to the amino acid asparagine at specific locations in the polypeptide chain. As the protein passes through the Golgi stack, the asparagine-linked oligosaccharides are modified to generate a diverse range of structures. Additional oligosaccharides may become linked to the amino acids serine and threonine. Although the particular oligosaccharide modifications are quite different in animal, plant, and fungal cells, the Golgi apparatus always functions as a “carbohydrate factory.” See Oligosaccharide

The Golgi apparatus also carries out other processing events, including the addition of sulfate groups to the amino acid tyrosine in some proteins, the cleavage of protein precursors to yield mature hormones and neurotransmitters, and the synthesis of certain membrane lipids such as sphingomyelin and glycosphingolipids. See Lipid, Protein

Golgi Apparatus

 

an intracellular reticular structure; the organelle associated with the synthesis of various inclusion bodies. Named for the Italian histologist C. Golgi.

The Golgi apparatus has a highly variable form; its appearance under the microscope varies from that of a complex netlike structure (a compact form occurring in vertebrates) to that of individual sinuous or rodlike bodies (a dispersed form, called a dictyosome, occurring in plants and invertebrates). Investigations with the electron microscope have shown that the Golgi apparatus comprises three elements: a system of (five to eight) flat cisternae (γ-membranes, 70–80 angstroms thick), vesicles (300–500 angstroms in diameter), and large vacuoles (0.2–0.3 microns in diameter). The Golgi apparatus is located near the nucleus or around the centrosome. On fixed material, it is revealed by impregnation with silver salts or osmic acid. The observation of living cells has confirmed the existence of the Golgi apparatus. The organelle contains lipids, lipoproteins, and phospholipids, but is relatively low in enzymes. The function of the Golgi apparatus is involved with the production of the various formed elements of the cell’s vital activities, such as secretory granules and vitelline lamellae, collagen, lipid, and glycogen inclusions, and melanosomol granules. Deposits of vital dyes, ascorbic acid, iron salts, and colloid silver are observed in the Golgi region. The activity of the Golgi apparatus is also implicated in the production of primary lysosomes. the acrosomes of spermatozoa, and the lamellae of plant cells. The role of the various components of the Golgi apparatus in these processes differs; the vesicles and cisternae are regarded as the functional parts of the Golgi apparatus, while the vacuoles only serve in the transport of substances. The dynamics of the incorporation of tagged amino acids confirm the fact that the Golgi apparatus is the final link in an intracellular “conveyor” that produces a protein secretion. The proteins synthesized on the ribosomes enter the Golgi apparatus through the cisternae of the endoplasmic reticulum, where they are concentrated and packed into granules. In the synthesis of protein products, the Golgi apparatus— the “packing plant”—forms the secretory granules. In the production of carbohydrates (mucopolysaccharides, glycoproteins), the intracellular “conveyor” in effect switches over to another product and the Golgi apparatus participates in the synthesis of polysaccharides. In mucus, bone, and cartilage cells, tagged sugar molecules are first incorporated into the Golgi apparatus and appear in other cell components only later. Sulfation, which is associated with the synthesis of acid mucopolysaccharides, also takes place in the Golgi apparatus.

REFERENCES

Rukovodstvo po tsitologii, vol. 1. Moscow-Leningrad, 1965. Pages 185–200.
Alov. I. A., A. I. Braude. and M. E. Aspiz. Osnovy funklsionainoi morfologii kletki. Moscow, 1966. Pages 82–113.

I. A. ALOV

Golgi apparatus

[′gȯl‚jē ‚ap·ə‚rad·əs]
(cell nad molecular biology)
A cellular organelle that is part of the cytoplasmic membrane system; it is composed of regions of stacked cisternae and it functions in secretory processes.
References in periodicals archive ?
The CLV_NDR_NDR_1 motifs matched with amino acid residues IRK (351-353) which is functional residue of N-Arg dibasic convertase (nardilysine) cleavage site (Xaa-|-Arg-Lys or Arg-|-Arg-Xaa) present in the extracellular, Golgi apparatus and cell surface.
Hu, "The role of GRASPs in morphological alterations of Golgi apparatus: mechanisms and effects," Reviews in the Neurosciences, vol.
All core 1 O-glycosylation structures have GalNAc as the first sugar in the series and, as depicted in Figure 2, tend to be localized within the cis region of the Golgi apparatus. C1GalT1 is expressed at lower levels in the cells from IgAN patients compared to controls.
The macrophage-like type A cells are characterized by the presence of a complex Golgi apparatus, vesicles, and vacuoles dispersed in the cytoplasm, scarce rough endoplasmic reticulum, and a dense pattern of nuclear chromatin and rare nucleoli.
The secretory function of the rods has been described earlier (Clement & Wurdak 1991), and in the present study we confirmed this finding, where transversal cuts allowed the visualization of a dense region with cytoplasmic content originated in the Golgi Apparatus (Clement & Wurdak 1991).
Incorporate the Golgi apparatus so that when the student has completed construction of the protein, they move on to the Golgi for processing or folding.
This sequence was initially thought to be crucial for localization of the whole toxin to the ER, but it is more probable that the KDEL sequence serves to enhance retrieval of dissociated CTA from the Golgi apparatus to the ER, instead of being essential for retrograde transport (35).
He told Keith Porter, who did pioneering work on the ultrastructure of cells and described the endoplasmic reticulum and confirmed the presence of the Golgi apparatus, that there was a statue of Camillo Golgi at the University of Pavia, Pavia, Italy.
The inner segmental layers are rich in membranous organelles such as Golgi apparatus and cisternae of rough endoplasmic reticulum, in addition to the previously mentioned myeloid bodies (Plate 6-33, 6-34).
[Ca.sup.2+] has also been shown to accumulate in endosomes, lysosomes, secretory granules, the Golgi apparatus, and nucleus (for review, see Laude and Simpson 2009).
Some glial cells showed disorganization of the Golgi apparatus. On week 9, an increase in the number of astrocytes was found and neurons appeared degenerated with swollen mitochondria and a vacuolated cytoplasm [10].
The fragmented neuronal Golgi apparatus in amyotrophic lateral sclerosis includes the trans-Golgi-network: functional implications.

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