Vesicle (biology and chemistry)

In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. If they have only one lipid bilayer, they are called unilamellar vesicles; otherwise they are called multilamellar. Vesicles store, transport, or digest cellular products and wastes.

This biomembrane enclosing the vesicle is the same as that of the outer cellular membrane. Then, because of the separation, the intravesicular environment can be made to be different from the cytosolic environment. Vesicles are a basic tool of the cell for organizing metabolism, transport, enzyme storage, as well as being chemical reaction chambers. Many vesicles are made in the Golgi apparatus, but also in the endoplasmic reticulum, or are made from parts of the plasma membrane.

Some types of vesicles

 * Transport vesicles are able to move molecules between locations inside the cell, e.g., proteins from the Rough Endoplasmic Reticulum to the Golgi Apparatus.


 * Synaptic vesicles located at presynaptic terminals in neurons store neurotransmitters.


 * Lysosomes (membrane-bound digestive vesicles) can digest macromolecules (break them down to small compounds) that were taken in from the outside of the cell by an endocytic vesicle.


 * Matrix vesicles are cell-derived microstructures involved in the initiation of biomineralization in a variety of tissues including bone, cartilage, dentin and turkey leg tendon. During normal calcification, a major influx of calcium and phosphate ions into the cells accompanies cellular apoptosis and matrix vesicle formation. Calcium-loading also leads to formation of phosphatidylserine:calcium:phosphate complexes in the plasma membrane mediated in part by a protein called annexins.  Matrix vesicles bud from the plasma membrane at sites of interaction with the extracellular matrix.  Thus, matrix vesicles convey to the extracellular matrix calcium, phosphate, lipids and the annexins which act to nucleate mineral formation. These processes are precisely coordinated to bring about mineralization at the proper place and time during bone development.

Vesicle coat
The vesicle coat serves to sculpt the curvature of a donor membrane, and to select specific proteins as cargo. It selects cargo proteins by binding to sorting signals. In this way the vesicle coat clusters selected membrane cargo proteins into nascent vesicle buds.

There are three types of vesicle coats: clathrin, COPI and COPII. Clathrin coats are mediate trafficking from the ER and plasma membrane. COPI coats are responsible for retrograde transport from the Golgi to the ER. COPII targets vesicles from the ER to the Golgi.