Mitochondria are the structures which produce energy within the organism’s cells, allowing them to function, enabling them to repair their lesions and care for themselves. Mitochondria fulfill several cellular functions, the best known being production of ATP (adenosine triphosphate), our cells’ fuel. Mitochondria are therefore an essential element of cellular respiration, which enables us to produce the energy we need. In some ways, mitochondria can be compared to a car’s engine. A cell cannot function without mitochondria, just as a car could not without an engine… They have their own DNA, and their own genes take part in mitochondrial operations. They always come from the mother, the male gamete in principle only carrying nuclear DNA.