AskDefine | Define lysosome

Dictionary Definition

lysosome n : an organelle found in the cytoplasm of most cells (especially in leukocytes and liver and kidney cells)

User Contributed Dictionary

English

Noun

  1. An organelle found in all types of animal cells which contains a large range of digestive enzymes capable of splitting most biological macromolecules.

Translations

digestive organelle

Extensive Definition

Lysosomes are organelles that contain digestive enzymes (acid hydrolases). They digest excess or worn-out organelles, food particles, and engulfed viruses or bacteria. The membrane surrounding a lysosome allows the digestive enzymes to work at the 4.5 pH they require. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, digesting their contents. They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus. The name lysosome derives from the Greek words lysis, which means dissolution or destruction, and soma, which means body. They are frequently nicknamed "suicide-bags" or "suicide-sacs" by cell biologists due to their role in autolysis. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949.
At pH 4.8, the interior of the lysosomes is more acidic than the cytosol (pH 7.2). The lysosome's single membrane stabilizes the low pH by pumping in protons (H+) from the cytosol via proton pumps and chloride ion channels. The membrane also protects the cytosol, and therefore the rest of the cell, from the degradative enzymes within the lysosome. For this reason, should a lysosome's acid hydrolases leak into the cytosol, their potential to damage the cell will be reduced, because they will not be at their optimum pH

Enzymes

Some important enzymes in these are:
Lysosomal enzymes are synthesized in the cytosol and the endoplasmic reticulum, where they receive a mannose-6-phosphate tag that targets them for the lysosome. Aberrant lysosomal targeting causes inclusion-cell disease, whereby enzymes do not properly reach the lysosome, resulting in accumulation of waste within these organelles.

Functions

The lysosomes are used for the digestion of macromolecules from phagocytosis (ingestion of other dying cells or larger extracellular material), endocytosis (where receptor proteins are recycled from the cell surface), and autophagy (wherein old or unneeded organelles or proteins, or microbes that have invaded the cytoplasm are delivered to the lysosome). Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis, of the cell, which means that the cell is digesting itself.
Other functions include digesting foreign bacteria (or other forms of waste) that invade a cell and helping repair damage to the plasma membrane by serving as a membrane patch, sealing the wound. Lysosomes also do much of the cellular digestion required to digest tails of tadpoles and to remove the web from the fingers of a 3- to 6-month-old fetus. This process of programmed cell death is called apoptosis.

Clinical relevance

There are a number of illnesses that are caused by the malfunction of the lysosomes or one of their digestive proteins, e.g., Tay-Sachs disease, or Pompe's disease. These are caused by a defective or missing digestive protein, which leads to the accumulation of substrates within the cell, impairing metabolism.

Additional images

cellular compartments and structures tagged with green fluorescent protein.

References

lysosome in Arabic: جسيم حال
lysosome in Catalan: Lisosoma
lysosome in Czech: Lyzozom
lysosome in Danish: Lysosom
lysosome in German: Lysosom
lysosome in Modern Greek (1453-): Λυσόσωμα
lysosome in Spanish: Lisosoma
lysosome in Esperanto: Lizosomo
lysosome in Persian: لیزوزوم
lysosome in French: Lysosome
lysosome in Galician: Lisosoma
lysosome in Korean: 리소좀
lysosome in Croatian: Lizosom
lysosome in Italian: Lisosoma
lysosome in Hebrew: ליזוזום
lysosome in Latvian: Lizosoma
lysosome in Luxembourgish: Lysosom
lysosome in Lithuanian: Lizosomos
lysosome in Hungarian: Lizoszóma
lysosome in Macedonian: Лизозом
lysosome in Dutch: Lysosoom
lysosome in Japanese: リソソーム
lysosome in Norwegian: Lysosom
lysosome in Occitan (post 1500): Lisosòma
lysosome in Polish: Lizosom
lysosome in Portuguese: Lisossomo
lysosome in Romanian: Lizozom
lysosome in Russian: Лизосома
lysosome in Slovak: Lyzozóm
lysosome in Slovenian: Lizosom
lysosome in Serbian: Лизозом
lysosome in Serbo-Croatian: Lizozom
lysosome in Finnish: Lysosomi
lysosome in Swedish: Lysosom
lysosome in Vietnamese: Lysosome
lysosome in Turkish: Lizozom
lysosome in Ukrainian: Лізосома
lysosome in Chinese: 溶體
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