Lysosomes: Digestive Compartments (Campbell Biology)
A lysosome is a membranous sac of hydrolytic enzymes that many eukaryotic cells use to digest (hydrolyze) macromolecules. Lysosomal enzymes work best in the acidic environment found in lysosomes. If a lysosome breaks open or leaks its contents, the released enzymes are not very active because the cytosol has a near-neutral pH. However, excessive leakage from a large number of lysosomes can destroy a cell by self-digestion.
Hydrolytic enzymes and lysosomal membrane are made by rough ER and then transferred to the Golgi apparatus for further processing. At least some lysosomes probably arise by budding from the trans face of the Golgi apparatus. How are the proteins of the inner surface of the lysosomal membrane and the digestive enzymes themselves spared from destruction? Apparently, the three-dimensional shapes of these proteins protect vulnerable bonds from enzymatic attack.
Lysosomes carry out intracellular digestion in a variety of circumstances. Amoebas and many other unicellular eukaryotes eat by engulfing smaller organisms or food particles, a process called phagocytosis (from the Greek phagein, to eat, and kytos, vessel, referring here to the cell). The food vacuole formed in this way then fuses with a lysosome, whose enzymes digest the food. Digestion products, including simple sugars, amino acids, and other monomers, pass into the cytosol and become nutrients for the cell. Some human cells also carry out phagocytosis. Among them are macrophages, a type of white blood cell that helps defend the body by engulfing and destroying bacteria and other invaders.
Lysosomes also use their hydrolytic enzymes to recycle the cell’s own organic material, a process called autophagy. During autophagy, a damaged organelle or small amount of cytosol becomes surrounded by a double membrane (of unknown origin), and a lysosome fuses with the outer membrane of this vesicle. The lysosomal enzymes dismantle the inner membrane with the enclosed material, and the resulting small organic compounds are released to the cytosol for reuse. With the help of lysosomes, the cell continually renews itself. A human liver cell, for example, recycles half of its macromolecules each week.
The cells of people with inherited lysosomal storage diseases lack a functioning hydrolytic enzyme normally present in lysosomes. The lysosomes become engorged with indigestible material, which begins to interfere with other cellular activities. In Tay-Sachs disease, for example, a lipid-digesting enzyme is missing or inactive, and the brain becomes impaired by an accumulation of lipids in the cells. Fortunately, lysosomal storage diseases are rare in the general population.
Urry, Lisa A.. Campbell Biology. Pearson Education. Kindle Edition. https://www.pearson.com/us/higher-education/series/Campbell-Biology-Series/2244849.html
Research Article: A Proteolytic Cascade Controls Lysosome Rupture and Necrotic Cell Death Mediated by Lysosome-Destabilizing Adjuvants
Date Published: June 3, 2014 Publisher: Public Library of Science Author(s): Jürgen Brojatsch, Heriberto Lima, Alak K. Kar, Lee S. Jacobson, Stefan M. Muehlbauer, Kartik Chandran, Felipe Diaz-Griffero, Teresa Frisan. http://doi.org/10.1371/journal.pone.0095032 Abstract: Recent studies have linked necrotic cell death and proteolysis of inflammatory proteins to the adaptive immune response mediated by the lysosome-destabilizing adjuvants, alum … Continue reading
Date Published: June 9, 2016 Publisher: Public Library of Science Author(s): Xiaochun Wu, Lingling Zhao, Zhi Chen, Xin Ji, Xianfeng Qiao, Yaping Jin, Wei Liu, Han-Ming Shen. http://doi.org/10.1371/journal.pone.0157100 Abstract: The intracellular amino acid pool within lysosome is a signal that stimulates the nutrient-sensing mTORC1 signalling pathway. The signal transduction cascade has garnered much attention, but … Continue reading
Research Article: The BH3 Mimetic Obatoclax Accumulates in Lysosomes and Causes Their Alkalinization
Date Published: March 7, 2016 Publisher: Public Library of Science Author(s): Vasileios A. Stamelos, Natalie Fisher, Harnoor Bamrah, Carolyn Voisey, Joshua C. Price, William E. Farrell, Charles W. Redman, Alan Richardson, Andreas Villunger. http://doi.org/10.1371/journal.pone.0150696 Abstract: Obatoclax belongs to a class of compounds known as BH3 mimetics which function as antagonists of Bcl-2 family apoptosis regulators. … Continue reading
Research Article: Giant Lysosomes as a Chemotherapy Resistance Mechanism in Hepatocellular Carcinoma Cells
Date Published: December 10, 2014 Publisher: Public Library of Science Author(s): Federico Colombo, Elena Trombetta, Paola Cetrangolo, Marco Maggioni, Paola Razini, Francesca De Santis, Yvan Torrente, Daniele Prati, Erminio Torresani, Laura Porretti, Matias A. Avila. http://doi.org/10.1371/journal.pone.0114787 Abstract: Despite continuous improvements in therapeutic protocols, cancer-related mortality is still one of the main problems facing public health. … Continue reading
Date Published: October 22, 2014 Publisher: Public Library of Science Author(s): Cristina I. López Sanjurjo, Stephen C. Tovey, Colin W. Taylor, Mohamed Trebak. http://doi.org/10.1371/journal.pone.0111275 Abstract: Inositol 1,4,5-trisphosphate (IP3) evokes release of Ca2+ from the endoplasmic reticulum (ER), but the resulting Ca2+ signals are shaped by interactions with additional intracellular organelles. Bafilomycin A1, which prevents lysosomal … Continue reading