18. Proteins are manufactured within the rough ER and lipids
and carbohydrates within the smooth ER. Often these molecules are in need of
further shaping (or joining to other subunits) to create the final product molecule.
The unfinished molecules move through the ER until they reach its end.
At that point, the ER pinches off, forming a small vacuole
or vesicle containing the molecules. This vesicle then moves to and then fuses
with the golgi apparatus where the final product molecule is made. The membranes
of the golgi apparatus then fold around the product to form a new vesicle.
This new vesicle then transports the product to where it is
needed. Sometimes this means the vesicle must fuse with the plasma membrane,
thus dumping the product molecules into the extracellular environment.
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Slichter