Lysosomes are subcellular organelles which perform many important cellular functions. For example, lysosomes digest foreign material and engulfed viruses and bacteria presenting in phagosomes during the process of phagocytosis. In addition, lysosomes destroy targeted organelles, such as mitochondria, and injured cells via autolysis. Autolysis plays a central role in many apoptotic cascades. Lysosomal functions are dependent on lysosomes fusing with target vacuoles and release of digestive enzymes. Lysosomes are also responsible for digesting protein from the cell surface presented via endocytosis.
Lysosomes are membrane-bound vesicles that contain digestive enzymes, such as glycosidases, proteases and sulfatases. Lysosomal enzymes are synthesized in the endoplasmic reticulum (ER), are transported to the Golgi apparatus, and are tagged for lysosomes by the addition of mannose-6-phosphate label. Malfunction of lysosomal enzymes can result in lysosomal storage diseases such as Tay-Sachs disease and Pompe's disease.