Lysosomes are small, spherical vesicles surrounded by a single membrane and containing powerful hydrolytic enzymes (hydrolases), such as proteases, lipases, carbohydrases and nucleases. They are made by the Golgi apparatus, which packages the enzymes into vesicles that bud off from its trans face. Lysosomes are about 0.1 to 1 µm across and look dense in electron micrographs.The inside of a lysosome is acidic (about pH 5), which is the optimum pH of its enzymes. The membrane keeps the enzymes separate from the rest of the cell, so they cannot digest the cell's own contents. Even if a few enzymes leak, they work poorly at the neutral pH of the cytosol.Functions
• Digesting material taken in by the cell: when a phagocyte engulfs a bacterium by phagocytosis, lysosomes fuse with the phagocytic vacuole and their enzymes hydrolyse the bacterium.
• Autophagy: breaking down old, worn-out organelles such as mitochondria. Useful products, such as amino acids, are released back into the cytoplasm and reused.
• Releasing enzymes outside the cell by exocytosis. The acrosome in the head of a sperm is a specialised lysosome whose enzymes digest the outer layers around the egg.
• Autolysis: the self-digestion of a whole cell, when lysosomes release their enzymes into the cytoplasm. This happens after cells die and also during development, for example removing the tissue between the fingers of an embryo.Phagocytes such as neutrophils contain especially large numbers of lysosomes.
• Digesting material taken in by the cell: when a phagocyte engulfs a bacterium by phagocytosis, lysosomes fuse with the phagocytic vacuole and their enzymes hydrolyse the bacterium.
• Autophagy: breaking down old, worn-out organelles such as mitochondria. Useful products, such as amino acids, are released back into the cytoplasm and reused.
• Releasing enzymes outside the cell by exocytosis. The acrosome in the head of a sperm is a specialised lysosome whose enzymes digest the outer layers around the egg.• Autolysis: the self-digestion of a whole cell, when lysosomes release their enzymes into the cytoplasm. This happens after cells die and also during development, for example removing the tissue between the fingers of an embryo.Phagocytes such as neutrophils contain especially large numbers of lysosomes.