I'm learning the basics of cell biology and one thing about the SNAP-SNARE complex is confusing me a lot.

I read that the SNAP-SNARE complex has nothing to do with endocytosis. But my question is: endocytosis and exocytosis both ultimately lead to the formation of a vesicle; and a vesicle, once formed, must fuse with a target membrane. The SNAP-SNARE complex mediates fusion of vesicles with target membranes, so wouldn't that mean that it controls the fusion of both endocytic and exocytic vesicles with their respective target membranes?

Am I making a gigantic blunder here? It would be great if someone could clarify this.


The very definitions of endocytosis and exocytosis seem to have been misunderstood here.

Endocytosis involves the cell membrane invaginating (folding inwards) and pinching off to form a vesicle containing some material present in the environment. This vesicle may then fuse with a lysosome and the material inside it will be degraded.

Exocytosis, on the other hand, involes the fusion of a vesicle inside the cell with the cell membrane to release its contents into the external environment.

So, endocytosis does not involve the process of fusion of a vesicle with a target membrane. The fusion of a vesicle with a target membrane is, in fact, exocytosis, and this process requires the SNAP-SNARE complex.

So, I think we are justified in claiming that the SNAP-SNARE complex pertains only to exocytosis.

Reference: Essential Cell Biology by Alberts et al

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