Mitochondrien, often referred to as the "powerhouses of the cell," are organelles found in nearly all eukaryotic cells. They are responsible for producing energy in the form of adenosine triphosphate (ATP) through a process called cellular respiration. This energy is essential for various cellular functions and activities. In addition to energy production, Mitochondrien play a role in regulating metabolism and apoptosis, or programmed cell death. They contain their own DNA, which is distinct from the cell's nuclear DNA, and can replicate independently. This unique feature supports the endosymbiotic theory, which suggests that Mitochondrien originated from ancient bacteria.