Golgi apparatus synthesis

Figure 25-2. The formation and secretion of (A) chylomicrons by an intestinal cell and (B) very low density lipoproteins by a hepatic cell. (RER, rough endoplasmic reticulum SER, smooth endoplasmic reticulum G, Golgi apparatus N, nucleus C, chylomicrons VLDL, very low density lipoproteins E, endothelium SD, space of Disse, containing blood plasma.) Apolipoprotein B, synthesized in the RER, is incorporated into lipoproteins in the SER, the main site of synthesis of triacylglycerol. After addition of carbohydrate residues in G, they are released from the cell by reverse pinocytosis. Chylomicrons pass into the lymphatic system. VLDL are secreted into the space of Disse and then into the hepatic sinusoids through fenestrae in the endothelial lining.

Figure 46-1. Diagrammatic representation of the two branches of protein sorting occurring by synthesis on (1) cytosolic and (2) membrane-bound polyribosomes. The mitochondrial proteins listed are encoded by nuclear genes. Some of the signals used in further sorting of these proteins are listed in Table 46-4. (ER, endoplasmic reticulum GA, Golgi apparatus.)...

The synthesis of the core proteins occurs in the endoplasmic reticulum, and formation of at least some of the above linkages also occurs there. Most of the later steps in the biosynthesis of GAG chains and their subsequent modifications occur in the Golgi apparatus. 

Like other cells, a neuron has a nucleus with genetic DNA, although nerve cells cannot divide (replicate) after maturity, and a prominent nucleolus for ribosome synthesis. There are also mitochondria for energy supply as well as a smooth and a rough endoplasmic reticulum for lipid and protein synthesis, and a Golgi apparatus. These are all in a fluid cytosol (cytoplasm), containing enzymes for cell metabolism and NT synthesis and which is surrounded by a phospholipid plasma membrane, impermeable to ions and water-soluble substances. In order to cross the membrane, substances either have to be very lipid soluble or transported by special carrier proteins. It is also the site for NT receptors and the various ion channels important in the control of neuronal excitability. 

Northcote DH, Pickett-Heaps JD. A function of the Golgi apparatus in polysaccharide synthesis and transport in the root-cap cells of wheat. 5ioc/iem J1966 98 159. 

Futerman, A.H., Stieger, B., Hubbard, A.L. and Pagano, R. E., 1990, Sphingomyelin synthesis in rat hver occurs predominantly at the ds and medial cistemae of the Golgi apparatus, /. Biol. Chem. 265 8650-8657... 

Maccioni, H. J., Daniotti, J. L., and Martina, J. A., 1999, Organization ofganghoside synthesis in the Golgi apparatus. Biochim Biophys Acta 1437 101-118. 

Other neurotransmitters are larger peptides, such as the enkephalins. These peptide neurotransmitters are synthesized in the cell body of the neuron, usually as part of larger polypeptides from which they are subsequently cleaved. Following synthesis, they are incorporated into secretory granules that bud off from the Golgi apparatus and are then transported down the axon to the terminals. 

Inhibits protein synthesis by interfering with endoplasmic reticulum and Golgi apparatus functions it also induces cell differentiation and caspase-dependent apoptosis Stabilizes protein structures and restores correct folding tiirough binding with tiiem... 

It seems likely that the enzyme complexes for hemicelluloses, pectins and cellulose are constructed, at least in part, on the endoplasmic reticulum and then transferred to the Golgi apparatus, where they are modified and sorted so that they can be segregated within the compartments of the Golgi cisternae (30,31). The complex for cellulose synthesis is not normally active within the Golgi apparatus and it is transported to active sites at the plasma membrane (1). The hemicelluloses and pectins are formed within vesicles and cisternae of the Golgi apparatus and the vesicles are transported to the plasma membrane, where fusion occurs and the polysaccharides are packed into the wall (1). It is not known whether particular polysaccharides such as the xylans of the hemicellulose and the arabinogalactans of the pectins are transported in separate vesicles or together in one vesicle. Nor is it known if the complex for cellulose synthesis is transported by vesicles which carry hemicellulose and pectin polysaccharides. 

Final stage in the synthesis of a neura-minidate-containing carbohydrate unit of a glycoprotein (human transferrin). This terminal glycosylation takes place in the Golgi apparatus. 

Brown, R. M., Herth, W., Franke, W. W., Romanovicz, D. The role of the Golgi apparatus in the biosynthesis and secretion of a cellulosic glycoprotein in Pleurochrysis a model system for the synthesis of structural polysaccharides. In Biogenesis of plant cell wall polysaccharides, pp. 207. Loewus, F. (ed.). New York Academic Press 1973... 

Role of glycosyltransferases The glycosyltransferases responsi ble for the stepwise synthesis of the oligosaccharides are bounc to the membranes of the ER or the Golgi apparatus. They act in i... 

The biosynthesis of O-Iinked oligosaccharides follows a different scheme. In contrast with the dolichyl pyrophosphate-mediated synthesis of N-linked oligosaccharides, the glycosyltransferases necessary for the synthesis of O-linked oligosaccharides are located in the Golgi apparatus [9]. Monosaccharide residues are added sequentially to the growing oligosaccharide chain. 

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