Although textbooks all call the mitochondria the "powerhouse of the cell," its roles go beyond simply generating energy. Mitochondria play an important role in sensing the health of the cell and mitochondrial dysfunction can lead to programmed cell death (apoptosis). Because of its role in apoptosis, mitochondrial dysfunction has been implicated in numerous diseases. One example is Parkinson's disease. When researchers tried to identify the mutation that causes an inherited form of the disease, they found that the mutation resides in a protein that resides in the mitochondria.