10.13.09 Lecture - Organelles

10.13.09 Lecture - Organelles - A tour of organelles II...

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10/13/09 A tour of organelles II Endoplasmic Reticulum: Functions: Docks ribosomes to site of membrane protein synthesis . Initial site for creating secreted proteins . Provides chaperones and special conditions for protein folding. Site of protein glycosylation for asparagine residues (N-glyc). Site of lipid bilayer assembly and lipid head group modification. Site of glycosylation for many specialized lipid head-groups. Site of Cop-II dependent vesicle budding. Bag of calcium ions for signaling pathways (sarcoplasmic reticulum). Basic Structure : The ER membrane is a single bilayer where lipids can be flipped from one side to the other. Rough ER contains docking sites for ribosomes that have a nascent signal peptide. The ER is a series of interconnected tubes and flattened membrane sheets. There does not appear to be an internal or external scaffolding. ER constantly buds off into vesicles. Vesicles constantly fuse with the ER. The ER is the principle site of new lipid insertion, but the shuffling mixes lipid composition up rapidly. Replication The ER can be devolved into vesicles and reconstituted in the cell. ER is probably reticulated by polymerizing microtubules. A (MT) tip attachment complex can pull new material out into long tubes, eventually covering much of the cytoplasmic volume. The Golgi Apparatus Function : The Gogli body makes complex polysaccharides. Glyco-proteins and proteo-glycans are manufactured in the Golgi. Golgi produces mucus.
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The interesting polysaccharides are built on N-glycosylated sites (from ER) by clipping, pruning, and assembly. The Golgi also can add a carbohydrate group to serine, threonine, or hydroxylysine (O-
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10.13.09 Lecture - Organelles - A tour of organelles II...

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