Mitochondrial DNA is
Closed circular
Nicked circular
Linear
Open circular
Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that conve chemical energy from food into a form that cells can use, adenosine triphosphate (ATP). Ref-Harpers illustrated biochemistry 30/e p585
Metabolism of nucleic acids