Mitochondrion is the singular form of mitochondria. The mitochondria major role is ATP production in the eukaryotic cell. These are mobile and flexible organelles, although in some cells they tend to stay in a fixed position. The fixed position is especially true of cells or locations in cells where there will be a need for a high amount of ATP production, such as, near flagella or between myofibrils of muscle. Mitochondria are also self-reproducing, they have their own circular DNA, with a slightly modified version of the codons. This differs with the eukaryote codon table.