Mitochondria

Mitochondria are elongated, fluid-filled sacs two to five micrometers long, which contain enzymes responsible for aerobic respiration. They often move slowly about in the cytoplasm and can produce others like themselves by dividing. They also contain a supply of DNA that seems to encode information for making a few kinds of RNA and protein molecules. The mitochondria also function in transforming energy into a form that is usable by cell parts. For this reason, they are sometimes called the "powerhouses" of cells.