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In cell biology, vesicles are miniscule membrane-enclosed sacs within the cell organelles of eukaryotic cells. These sacs help transport or absorb proteins, enzymes and other cell necessities. Inside the membrane sac of a vesicle are macromolecules that require the ability to move beyond cell walls. The membrane encompassing the sac fuses with the outer cell wall to allow these macromolecules to pass through. Vesicles are important parts of human cells, although they also appear in other multicellular organisms.
Eukaryotic cells are the only cells to have vesicles. These cells are a specific type of cell in which various internal parts, called cell organelles, are contained separately inside membranes. Cell organelles have specific functions in maintaining individual eukaryotic cells. Eukaryotic cells are unique to multicellular organisms, differing from single-cell organisms with prokaryotic cells that have no nucleus.
The cell organelles of eukaryotic cells require a transportation system in order to exchange essential materials. Depending on the type of cell, vesicles transport proteins or enzymes, absorb food cells, store and release neurotransmitters or perform a number of other functions for organelles. The cell type and purpose determine the specific function of a vesicle.
Human, plant and animal cells use a variety of types of vesicles, depending on the type of cell and its specific intended function. For example, lysosomes are a type of vesicle needed for digestion. Lysosomes hold enzymes needed to break down food cells. As food is absorbed, a lysosome vesicle bonds to the vesicle holding the food cell, releasing its enzymes through a process called phagocytosis. These enzymes break down food cells into smaller parts for absorption by other cells.
Secretory vesicles are commonly associated with nerve cells in a human or animal. These membranes hold neurotransmitters. The nervous system triggers these components through hormonal signals. Through the process of exocytosis, the secretory vesicle’s outer membrane fuses to the nerve terminal, releasing neurotransmitters into the space between nerve endings known as the synaptic cleft. Neurotransmitters carry information from one nerve ending to the next, traveling along the central nervous system to the brain.
As internal cell mechanisms, vesicles perform transportation, absorption and storage functions imperative to numerous bodily functions. Without these miniscule membrane sacs, cells would be unable to exchange materials needed to maintain healthy cell development and crucial system processes. In short, without vesicles, human and other multicellular organisms could not exist, because the crucial chemical cell processes needed would have no method by which to exchange essential materials.
@pastanaga - That's actually quite a good way of remembering!
A vesicle is just a bubble of liquid inside another liquid. I always thought of them as being quite complex and marveled that the cell could even create them, but when it comes right down to it, they are quite simple (but no less elegant for it).
Of course, there are several different types of cellular vesicles and their function and form depends on what kind they are.
When I was studying cell biology it helped me to remember that vesicles are one of the ways of transporting things around the cells, and that the word sounds similar to "vehicles".
I know that's a bit of a stretch, but it helped me to remember what they are, so it served its purpose.
To this day I imagine transport vesicles looking like minis. They are kind of the right shape for it!