Organelles: (1) nucleolus(2) nucleus (3) ribosomes (little dots) (4) vesicle (5) rough endoplasmic reticulum(ER) (6) Golgi apparatus(7) Cytoskeleton(8) smooth ER (9) mitochondria (10) vacuole(11) cytoplasm(12) lysosome(13) centrioles within centrosome] In general, vacuole functions include:
* Removing unwanted structural debris
* Isolating materials that might be harmful or a threat to the cell
* Containing waste products
* Maintaining internal
hydrostatic pressureor turgorwithin the cell
* Maintaining an
* Containing small molecules
* Exporting unwanted substances from the cell
Vacuoles also play a major role in
autophagy, maintaining a balance between biogenesis(production) and degradation (or turnover), of many substances and cell structures. Vacuoles store food and other materials needed by a cell. They also aid in destruction of invading bacteriaor of misfolded proteins that have begun to build up within the cell. The vacuole is a major part in the plant cell.
plant cells have one or several vacuoles that typically occupy more than 30% of the cell's volume, and that can occupy as much as 90% of the volume for certain cell types and conditions. [Alberts, Bruce, Johnson, Alexander, Lewis, Julian, Raff, Martin, Roberts, Keith, and Walter, Peter (2002). "Molecular Biology of the Cell (Fourth Edition)," (Garland Science, New York), p. 740.] A vacuole is surrounded by a membrane called the tonoplast.
This vacuole houses large amounts of a liquid called
cell sap, composed of water, enzymes, inorganic ions (like K+ and Cl-), salts (such as calcium), and other substances, including toxic byproducts removed from the cytosol to avoid interference with metabolism. Toxins present in the vacuole may also help to protect some plants from predators. Transport of protons from cytosol to vacuole aids in keeping cytoplasmic pHstable, while making the vacuolar interior more acidic, allowing degradative enzymes to act. Although having a large central vacuole is the most common case, the size and number of vacuoles may vary in different tissues and stages of development. Cells of the vascular cambium, for example, have many small vacuoles in winter, and one large one in summer.
Aside from storage, the main role of the central vacuole is to maintain
turgorpressure against the cell wall. Proteins found in the tonoplast control the flow of water into and out of the vacuole through active transport, pumping potassium(K+) ions into and out of the vacuolar interior. Due to osmosis, water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, the cell will plasmolyse. Turgor pressure exerted by vacuoles is also helpful for cellular elongation: as the cell wall is partially degraded by the action of auxins, the less rigid wall is expanded by the pressure coming from within the vacuole. Vacuoles can help some plant cells to reach considerable size. Another function of a central vacuole is that it pushes all contents of the cell's cytoplasm against the cellular membrane, and thus keeps the chloroplastscloser to light.
The vacuole also stores the
pigments in flowers and fruits.
Vacuoles in animals are a part of the processes of
exocytosisand endocytosis. Exocytosis is the extrusion process of proteins from the Golgi apparatusinitially enter secretory granules, where processing of prohormonesto the mature hormones occurs before exocytosis, and also allows the animal cell to rid waste products.Endocytosis is the reverse of exocytosis. There are various types. Phagocytosis("cell eating") is the process by which bacteria, dead tissue, or other bits of material visible under the microscope are engulfed by cells. The material makes contact with the cell membrane, which then invaginates. The invaginationis pinched off, leaving the engulfed material in the membrane-enclosed vacuole and the cell membrane intact. Pinocytosis("cell drinking") is essentially the same process, the difference being that the substances ingested are in solution and not visible under the microscope cite journal | author = William F. Ganong, MD | title = REVIEW OF MEDICAL PHYSIOLOGY - 21st Ed. | year = 2003]
Hydropic (vacuolar) changes are of importance of identifying various pathologies, such as the reversible cell swelling in renal tubules caused by
hypoperfusionof the kidneysduring open heart surgery.
* (2003) Lange Medical Books/McGraw-Hill, Medical Publishing Division, New York
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