This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
Mitochondrial DNA is 
Select and explain. 
A. Closed circular, B. Nicked circular, C. Linear, D. Open circular
A: Closed circular
Answer: A: Closed circular 
Explanation: 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