Vesicle
A vesicle is a small membrane-bound sac that transports, stores, releases, or digests material inside cells and between cellular compartments.
What a vesicle is
A vesicle is a small sac surrounded by a lipid membrane. Cells use vesicles to move cargo, store molecules, digest material, recycle membrane, and communicate with the outside world. Because the vesicle membrane is built like other cellular membranes, it can bud from one membrane and fuse with another.
Cargo and membranes
A vesicle can carry soluble proteins, membrane proteins, lipids, enzymes, signaling molecules, waste, or material taken in from outside the cell. Its membrane keeps cargo separated from the cytoplasm while also carrying proteins that help identify where the vesicle came from and where it should go.
Budding and coats
Many vesicles form by budding from a donor membrane. Protein coats can help bend the membrane, choose cargo, and pinch off the new vesicle. After budding, the coat may come off so the vesicle can move, dock, and fuse with the correct target membrane.
Transport through the endomembrane system
Transport vesicles connect the endoplasmic reticulum, Golgi apparatus, lysosomes, plasma membrane, and other compartments. A newly made secreted protein may enter the ER, travel in vesicles to the Golgi, be modified and sorted, and then leave in another vesicle for secretion or delivery to a cellular destination.
Endocytosis
In endocytosis, the cell membrane folds inward to bring material into the cell inside a vesicle. This can help cells take up nutrients, regulate surface receptors, sample the environment, or engulf larger material in specialized cells. Incoming vesicles often mature or fuse with endosomal and lysosomal compartments.
Exocytosis
In exocytosis, a vesicle moves to the plasma membrane and fuses with it. Cargo can then be released outside the cell, and vesicle membrane becomes part of the cell surface. Secretory vesicles release hormones, digestive enzymes, antibodies, neurotransmitters, mucus, and many other products.
Movement and targeting
Vesicles do not simply drift at random. Cytoskeletal tracks and motor proteins can move them through the cell, while molecular tags and tethering proteins help them dock at the right destination. Fusion proteins then bring membranes together so cargo delivery is specific rather than chaotic.
Why it matters
Vesicles matter because cells are organized by traffic as much as by structure. Without vesicles, proteins could not be sorted efficiently, membranes could not be renewed, signals could not be secreted on demand, and many forms of digestion, recycling, immunity, and nerve communication would fail.