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Lecture 9
Intracellular Vesicular Transport Part 3: Vesicle Transport From the TGN,
Endocytosis
Exocytosis: Transport from the TGN to the Plasma Membrane
oExocytosis
Fusion of transport vesicles from Golgi network with
plasma membrane
oTransport vesicles
Lipids
Membrane proteins
Secreted soluble proteins
Exocytosis: 2 Types of Secretory Pathways
o1) Constitutive secretory pathway no regulation
o2) Regulated secretory pathway vesicles bud off Golgi and
dont fuse with plasma immediately
1) Constitutive Secretory Pathway
oDefault pathway for proteins that do not have a sorting signal
oVesicles bud of Golgi and fuse with plasma membrane
oEg. Release of antibodies by activated B lymphocytes
2) Regulated Secretory Pathway
oWaits for signal to fuse with plasma membrane
oProteins in secretory vesicles
In cytosol near plasma membrane
oSignal: eg. Increased intracellular [Ca2+]
Vesicles fuse with plasma membrane
Signal may be a hormone or neurotransmitter
oHow are proteins sorted to vesicles?
Found as aggregates in TGN
2) Regulated Secretory Pathway cntd
oeg. Insulin
Secreted from pancreatic beta-cell
Elevation in blood glucose
Increased intracellular [Ca2+] signal
Vesicles fuse with plasma membrane
Endocytosis: Transport From the Plasma Membrane to the Early
Endosome
oEndocytosis
Transport into cell from plasma membrane
oTake up macromolecules eg. Cholesterol
oDown-regulate signaling pathways
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