User:SaxofThunder/Membrane vesicle trafficking


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Movement within cells
Once vesicles are produced in the endoplasmic reticulum and modified in the golgi body they make their way to a variety of destinations within the cell. Vesicles first leave the golgi body and are released into the cytoplasm in a process called budding. Vesicles are then moved towards their destination by motor proteins. Once the vesicle arrives at its destination it joins with the bi-lipid layer in a process called fusion, and then releases its contents.

Budding
Receptors embedded in the membrane of the golgi body bind specific cargo (such as dopamine) on the lumenal side of the vesicle. These cargo receptors then recruit a variety of proteins including other cargo receptors and coat proteins such as clathrin, COPI and COPII. As more and more of these coating proteins come together, they cause the vesicle to bud outward and eventually break free into the cytoplasm. The coating proteins are then shed into the cytoplasm to be recycled and reused.

Motility between cell compartments
For movement between different compartments within the cell, vesicles rely on the motor proteins myosin, kinesin (primarily anterograde transport) and dynein (primarily retrograde transport). One end of the motor proteins attaches to the vesicle while the other end attaches to either microtubules or intermediate filaments. The motor proteins then move by hydrolyzing ATP, which propels the vesicle towards its destination.

Docking and Fusion
As a vesicle nears its intended location, RAB proteins in the vesicle membrane interact with docking proteins at the destination site. These docking proteins bring the vesicle in closer to interact with the SNARE Complex found in the target membrane. The SNARE complex reacts with synaptobrevin found on the vesicle membrane. This forces the vesicle membrane against the membrane of the target complex (or the outer membrane of the cell) and causes the two membranes to fuse. Depending on whether the vesicle fuses with a target complex or the outer membrane, the contents of the vesicle are then released either into the target complex or outside the cell.