These are subcellular organelles, approximately of the same size as small mitochondria. They are bound by a membrane and appear as bags filled with digestive enzymes such as ribonuclease, glycosidase, acid phosphatase, and aryl sulphates. The structure of lysosome is as shown in Figure 1.6. As long as the membrane of lysosome remains intact, the enzymes within lysosomes are unable to act on substrates in the cytoplasm. Once the membrane is ruptured, release of lysosomal enzymes is followed by dissolution of the cell (autophagy), Therefore, lysosomes are called suicide bags. The main function of lysosomes is intracellular and extracellular digestion. Acid phosphatase is the marker enzyme.