Exocytosis Flashcards
What is the constitutive pathway?
In all cells transport vesicles depart trans Golgi network to plasma membrane (TGN)
What is the regulated secretory pathway?
Specialized secretory cells use a second pathway - proteins stored in secretory vesicles
What is protein sorting?
proteins leaving Golgi network sorted into 3 classes based on their destination
What are the 3 pathways?
- Lysosomes (by Mannose-6-phosphate)
- Regulated secretory pathways
- Proteins lacking signals use constitutive pathway
Where does protein aggregation occur in regulated secretory pathways?
Ionic environment of trans Golgi network
Where does the signal bind to?
Surface receptor
What does surface receptor binding intiate?
Exocytosis of secretory products
What are the two steps of exocytosis?
Docking
Fusion
How are peptide neurotransmitters transported?
Packaged in vesicles and transported down axon along microtubule
What is full collapse secretion?
Secretory vesicles completely merge with plasma membrane before release
Vesicles then retrieved by endocytosis
What is the Kiss-and-run model?
Vesicles can transiently dock and expel contents without full plasma membrane fusion
Vesicles can then be refilled
What are porosomes?
Cup-shaped lipoprotein complexes found in plasma membrane of eukaryotic cells
What is the function of porosomes?
Sites where secretory vesicles transiently dock in the fusion of vesicle fusion and secretion
What happens when synaptic vesicles dock at porosome base?
Develop intravesicular pressure (swell) via active transport of water through AQP
How do synaptic vesicles fuse to porosome base?
Via SNARES and calcium
What is the effect of an action potential a function of?
Quantal size, or amplitude
Mean number of quanta released
What is a key requirement for quantal release?
Concentration of neurotransmitter in vesicles
What is the vacuolar proton pump?
Multi-subunit ATPase - creates transmembrane electrochemical gradient
Gradient acts as an energy source for active uptake of transmitter
What is the neurotransmitter-specific vesicular transporter?
Intergral membrane protein
12 membrane spanning domains
What is a mediator of release?
Calcium
What are vesicles held in place by on the presynaptic terminal?
Ca2+ sensitive vesicle membrane proteins (vamps) eg. Synapsin 1
What does elevated Ca levels activate?
CaMKII which phosphorylates Synapsin 1 - releases calcium from actin cage
What trafficks the vesicle?
G-protein Rab3A
What are th4 SNARE proteins involved in vesicle priming?
Synaptobrevin
Syntaxin
SNAP25
Synaptotagmin
What does Ca2+ activation of Synaptotagmin cause?
Causes it to bind to SNARE protein
What 6 proteins are involved in transmitter release?
v-SNARE
t-SNARE
Synaptotagmin
Synaptobrevin
Syntaxin
SNAP25
What disassembles the SNARE complex?
ATPase NSF and SNAP
