Steps involved: Synaptic Vesicle Exocytosis
I . Trafficking: Vesicles are transported to the cell membrane along microtubules of the cytoskeleton. Movement of the vesicles is powered by the motor proteins kinesins, dyneins, and myosins.
II. Tethering: Upon reaching the cell membrane, the vesicle becomes linked to and pulled into contact with the cell membrane.
III. Docking: Involves the attachment of the vesicle membrane with the cell membrane. The phospholipid bilayers of the vesicle membrane and cell membrane begin to merge.
IV. Priming: Priming occurs in regulated exocytosis and not in constitutive exocytosis. This step involves specific modifications that must happen in certain cell membrane molecules for exocytosis to occur. These modifications are required for signaling processes that trigger exocytosis to take place.
V. Fusion: There are two types of fusion that can take place in exocytosis. In complete fusion, the vesicle membrane fully fuses with the cell membrane. The energy required to separate and fuse the lipid membranes comes from ATP. The fusion of the membranes creates a fusion pore, which allows the contents of the vesicle to be expelled as the vesicle becomes part of the cell membrane. In kiss-and-run fusion, the vesicle temporarily fuses with the cell membrane long enough to create a fusion pore and release its contents to the exterior of the cell. The vesicle then pulls away from the cell membrane and reforms before returning to the interior of the cell.
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