Lysosom

Lysosom, commonly spelled lysosome, is a membrane-bound organelle in most animal cells, and in some other eukaryotes, that contains an array of hydrolytic enzymes responsible for breaking down biological polymers. The lysosome lumen is acidic, with a pH around 4.5 to 5.0, which optimizes enzyme activity and keeps the enzymes safely sequestered from the cytosol.

Lysosomal enzymes are synthesized in the endoplasmic reticulum, modified in the Golgi with mannose-6-phosphate tags, and delivered to lysosomes via vesicles. The lysosome lumen maintains acidic pH of about 4.5 to 5.0 by V-ATPases. The lysosome membrane contains transporters that export breakdown products to the cytosol.

Lysosomes digest macromolecules from endocytosis, phagocytosis, and autophagy; they recycle damaged or unnecessary organelles via autophagy and contribute to immune defense.

Defects in lysosomal enzymes lead to lysosomal storage disorders (for example Gaucher and Tay-Sachs diseases) characterized by accumulation of substrates. Treatments include enzyme replacement therapy, substrate reduction, and, in some cases, gene therapy.

In addition to digestion, lysosomes participate in cellular signaling and metabolism, notably in the mTOR pathway, coordinating growth and nutrient sensing with lysosomal function.