A
vacuole is a
membrane organelle which is present in all
plant and
fungal cells and some
protist,
animal[1] and
bacterial cells.
[2] Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules including various
enzymes in
solution, though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membrane
vesicles and are effectively just larger forms of these.
[3] The organelle has no basic shape or size, its structure varies according to the needs of the cell.
The function and importance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain protists than those of animals and bacteria. In general, the functions of vacuole include
Vacuoles also play a major role in autophagy, maintaining a balance between biogenesis (production) and degradation (or turnover), of many substances and cell structures in certain organisms. They also aid in destruction of invading bacteria or of misfolded proteins that have begun to build up within the cell. In protists, vacuoles have the additional function of storing food which has been absorbed by the organism, and assist in the digestive and waste management process for the cell.[4]
Large central vacuoles are found in three genera of filamentous sulfur bacteria, the Thioploca, Beggiatoa and Thiomargarita. The cytoplasm is extremely reduced in these genera and the vacuole can occupy between 40-98% of the cell.[5] The vacuoles contain high concentrations of nitrate ions and is therefore thought to be a storage organelle.[6]
