The powerhouse of the cell is known as the mitochondrion. Mitochondria are responsible for producing adenosine triphosphate (ATP), which is the primary energy currency of cells. Through the process of cellular respiration, mitochondria convert nutrients into usable energy. They play a critical role in metabolic processes and are involved in regulating cell growth and apoptosis. Mitochondria have their own DNA and are thought to have originated from ancient symbiotic bacteria.