Lysosomes are organelles in eukaryotic cells that contain digestive enzymes to digest macromolecules. They are built in the Golgi apparatus. At pH 5, the interior of the lysosomes is more acidic that the cytosol (pH 7). The lysosome membrane stabilizes the low pH by pumping in protons (H+) from the cytosol, and also protects the cytosol, and therefore the rest of the cell, from the digestive enzymes within the lysosome. The digestive enzymes need the acidic environment of the lysosome to function correctly. All these enzymes are produced in the endoplasmic reticulum, and transported and processed through the Golgi apparatus. The Golgi apparatus produces lysosomes by budding (budding means unequal division, resulting in one large and one small membrane-enclosed space). The most important enzymes in lysosomes are:
- Lipase, which digests lipids,
- Carbohydrases, which digest carbohydrates (e.g., sugars),
- Proteases, which digest proteins,
- Nucleases, which digest nucleic acids.