Lysosomes contain digestive substances that break down foreign matter. The digestive substances in lysosomes are enzymes made in the ribosomes, types of organelles that make proteins and are found on a structure called the rough endoplasmic reticulum. These enzymes are packaged into lysosomes by other organelles called Golgi apparati.
The enzymes in lysosomes break down biological substances, such as proteins, carbohydrates, fats and nucleic acids. These substances can come from an old organelle, a food source or a foreign agent, such as a virus.
Primary lysosomes originate in the Golgi apparatus. These lysosomes fuse with phagosomes to become secondary lysosomes. Phagosomes are vesicles that form when a part of a cell's plasma membrane envelops and engulfs a food particle. The digestive enzymes then enter the phagosome from the fusing of the lysosome, thus breaking down the contents of the phagosome.