2.16 notes (1).doc

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Published on 21 Aug 2012
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Golgi Apparatus: items enter from ER on the cis-Golgi, next is the medial Golgi and
then trans-Golgi (also called TGN = trans Golgi network)
-increases in acidity towards the trans Golgi (trans = 6.5 pH)
-various Golgi enzymes are localized to different compartments of the Golgi
-cisternae are detaching and peeling off the TGN
-stacks consist of layered cisternae (like stack of pancakes)
-Golgi enzymes (most notably those that modify N-linked oligosaccharides) are local-
ized sharply to particular regions of the Golgi
-Stacks are arranged in long ribbons with disorganized areas between the stacks
Functions of the Golgi:
1) Sequential modifications of N-linked oligosaccharides
-glucose is trimmed off in ER, and sugars are added in the Golgi (ends with negative
charge), different enzymes must work in sequence in the Golgi
-functions occur at different places in the ER
2) O-linked glycosylation and Proteoglycan glycosylation
-N-acetyl-galactosamine linked to serine (often just before glycine) or to threonine gets
sugars added to it in the Golgi
-in proteoglycans this can continue until there is a chain of 100+ repeating saccharide
units (these can be further modified by sulphation)
-secreted proteoglycans form a large portion of extracellular matrix
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2) Proteolytic modifications to proteins (late Golgi) -- acidic TGN can cut amino acids
3) Sorting of proteins to various destinations (late Golgi)
4) Production of secretory granules (late Golgi) -- these break off of the cistarane, vac-
uoles which bud off TGN acidified and full of densely packed enzymes forming gran-
ules
-cisternal maturation is the hypothesis that is now favored
All exit from the Golgi is from the trans face (except for retrograde trafficking to
the ER)
-multiple pathways exist (both coated vesicles -- clathrin -- and tubular transport inter-
mediates)
-Golgi - central sorting station
-endosomes = transport intermediates form from trans-Golgi
Tubular transport intermediates exit via apical end, clathrin exits basolateral end
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Document Summary

Golgi apparatus: items enter from er on the cis-golgi, next is the medial golgi and then trans-golgi (also called tgn = trans golgi network) Increases in acidity towards the trans golgi (trans = 6. 5 ph) Various golgi enzymes are localized to different compartments of the golgi. Cisternae are detaching and peeling off the tgn. Stacks consist of layered cisternae (like stack of pancakes) Golgi enzymes (most notably those that modify n-linked oligosaccharides) are local- ized sharply to particular regions of the golgi. Stacks are arranged in long ribbons with disorganized areas between the stacks. Functions of the golgi: sequential modifications of n-linked oligosaccharides. Glucose is trimmed off in er, and sugars are added in the golgi (ends with negative charge), different enzymes must work in sequence in the golgi. Functions occur at different places in the er: o-linked glycosylation and proteoglycan glycosylation.

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