Diagram of a simple vesicle (liposome). (Source: Wikimedia Commons)
Episode 6 - Vesicles
Vesicles are a variety of small, membrane-bound sacs in the cytoplasm of cells that function in the transport, storage and digestion of substances, or in some other activity. There are many types of vesicles, including food vacuoles, large central vacuoles, storage vesicles, transport vesicles, and vesicles that are responsible for the break-down of substances, including lysosomes and peroxisomes.
Diagram of a simple vesicle (liposome). (Source: Wikimedia Commons)
Vesicles play a major part in the endomembrane system of eukaryotic cells. There, they transport unfinished proteins and lipids, through the cytoplasm, from the endoplasmic reticulum to the Golgi body, and from the Golgi to the cell membrane. Since the phospholipid bilayer is fluid, the phospholipid molecules of the cell membrane and the vesicle membrane can easily fuse with each other. Once the transport vesicle reaches the cell membrane, it forges with the cell membrane and releases these finished products by the process of excocytosis. During endocytosis, particles too big to dissolve though the membrane are transported into the cell via the formation of a new vesicle around the particles. The new vesicle then buds off from the plasma membrane and enters into the cytoplasm, where it fuses with lysosomes and peroxisomes and other digestion vesicles, and these vesicles digest the contents of the transport vesicle.
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