What Are Lysosomes?

Posted on 27 Sep 2011 20:50

Lysosomes are sac-like organelles, found in animal cells, which are surrounded by a membrane and rich in hydrolytic (acid hydrosolate) enzymes. These organelles function as an intracellular digestive system or a "degradative compartment" within eukaryotic cells. 1, 2

Materials within the cell which need to be digested are deposited within the lysosomes. These materials may be organelles that have ceased to function, food particles taken cells by endocytosis, or even foreign bodies such as bacteria. 3

Function of Lysosomes

Containing more than 50 types of acid hydroxylases, among which are proteases, lipases, nucleases, polysaccharidases. These are capable of splitting complex molecules, lysosomes digest various proteins, nucleic acids, mucopolysaccharides, lipids, and glycogen.

Lysosomes are of chief importance in macrophages and leukocytes,destoyers of bacteria and viruses, where lysosomal organelles are large and abundant. They also function in autophagy which, by degrading degrading cell components is essential to the normal function and life of as it recycles cellular materials and maintains cell homeostasis. 1, 2

Lysosomes are also involved in autolysis, which digests dispensable cellular components. This is important, for example, for mitochondria, which degrade and must be renewed often. In phagocytosis, lysosomes are involved in digestion and foreign substances taken up by the cell. This may serve to render dangerous substances harmless, as when lysosomal phagocytosis protects against invading bacteria during the healing of a wound. 4


Lysosome Structure

Lysosomes have an acid pH (5), much more acid than the cytoplasm, and thus rely on materials being reposited into the membrane so that the hydroxylases can function. Although most organelles are identified by shape and structure, it is the presence of lysosomal hydrosolases and integrated membrane glycoproteins which defines these structures, rather than a certain shape or structure. Lysosomes usually apper as a spherical body but are also sometimes seen to be long tubules, such as those in fibroblasts and macrophages. 2 These structures are believed to form by the combined activities of the endoplasmic reticulum and the Golgi apparatus, forming a very tightly packed membrane of lytic enzymes. This membrane is capable of selectively fusing with other cell vesicles, allowing wastes to be removed by exocytosis so that they can be digested or catabolized. 4

1. Medeiros, Denis M. Advanced Human Nutrition. Sudbury, MA: Jones & Bartlett Learning, 2012.
2. Mullins, Chris. The Biogenesis of Cellular Organelles. Georgetown, TX: Landes Bioscience/Eurekah.com, 2005. 111.
3. Kimball, John W. "Lysosomes and Peroxisomes." Kimball's Biology Pages. Web. 27 Sept. 2011. <http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/L/Lysosomes.html>.
4. Groff, James L., and Sareen Annora Stepnick. Gropper. Advanced Nutrition and Human Metabolism. Belmont, CA: West/Wadsworth, 2000. 11-12.

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