Lysosomes

Lysosomes are small, round bodies containing digestive enzymes that break down large food molecules into smaller ones. They are found in the cytoplasm, or jelly-like fluid, of all eukaryotic cells (cells with a distinct nucleus). Lysosomes are the main site where digestion takes place inside a cell.

As organelles or specialized, membrane-bound structures inside a cell that have a certain job to do, lysosomes contain very powerful enzymes called "hydrolases" that are capable of breaking down many different types of substances. These enzymes work on food molecules such as proteins, carbohydrates, and fats and quickly break them down into smaller particles that can be easily used by the cell. The powerful enzymes in lysosomes are also sometimes put to another use by the cell when it needs to rid itself of a damaged or defective organelle. In such a case, the lysosomes attack an organelle and quickly break it down and destroy it. At other times, a cell may use lysosomes to actually destroy itself. This process is known as "autolysis" (auto means "self" and lysis means "destruction"). This usually happens for a very good reason, as in metamorphosis when an animal has to entirely reshape its tissues (as when a caterpillar changes into a butterfly). While biologists know that lysosomes are used by the cell to digest the food it takes in, they do not yet fully understand how the lysosome membrane itself avoids being broken down by the enzymes it carries. This is especially puzzling since the membrane is made of the same compounds that the enzymes easily destroy.

[See alsoCells; Enzymes ]