Lysosomes


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Related to Lysosomes: mitochondria, endoplasmic reticulum, Peroxisomes

Lysosomes

 

structures in animal and plant cells, 0.25–0.50 microns in size, that contain about 40 enzymes capable of decomposing (lysing) proteins, nucleic acids, polysaccharides, and lipids.

Lysosomes were discovered in 1955 by the Belgian biochemist C. De Duve. They are characterized principally by the presence of enzymes of the acid hydrolase group and by a single-layered lipoprotein membrane that protects the compounds in the cell from the destructive action of the lysosomal enzymes. There are two main types of lysosomes: primary lysosomes, which serve as receptacles for enzymes but are not involved in intracellular digestion; and secondary lysosomes, which are associated with the lytic processes. Secondary lysosomes form by the merger of primary lysosomes with vacuoles containing material used for digestion. They include cytolysosomes, in which the cell components proper are digested—a process called autophagy.

Figure 1. Diagram of development of primary and secondary lysosomes: (1) granular endoplasmic reticulum, (2) Golgl complex, (3) primary lysosomes, (4) plasma membrane, (5) formation of pinocytic vesicle, (6) formation of phagocytic vesicle, (7) food vacuole, (8) cytolysosome, (9) nucleus

It is thought that the membranes of lysosomes either form specially or form from the endoplasmic reticulum or the Golgi complex. The synthesis of lysosomal enzymes probably occurs in what is called the intracellular conveyor system: ribosome— endoplasmic reticulum—Golgi complex.

Lysosomes have digestive, protective, and excretory functions in the cell. Their role in intracellular digestion is especially pronounced in cells capable of pinocytosis and phagocytosis. Lysosomes also play a role in a number of physiological processes requiring the lysis of cell structures, such as the postpartum involution of the uterus; the protection of the cell from bacteria, foreign bodies, and chemical substances; inflammatory and immunological reactions; and dystrophy and necrosis. The development of systemic lupus erythematosus, rheumatism, rheumatoid arthritis, a number of diseases of the liver and kidneys, and malignant neoplasms is associated with the action of lysosomal factors.

REFERENCES

Znachenie lizosom ν fiziologicheskikh i patologicheskikh protsessakh. Moscow, 1968.
Allison, E. “Lizosomy i bolezni.” In the anthology Molekuly i kletki, fasc. 4. Moscow, 1969. Pages 196–213. (Translated from English.)
Alov, I. A., A. I. Braude, and M. E. Aspiz. “Lizosomy.” In their book Osnovy funktsional’noi morfologii kletki, 2nd ed. Moscow, 1969. Pages 133–42.
Aspiz, M. E., and M. A. Starosvetskaia. “Lizosomy.” In Itogi nauki: Seriia Biologiia: Tsitologiia, Obshchaia genetika, Genetika cheloveka, 1970. Moscow, 1971. Pages 71–101.
M. E. ASPIZ
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