Nuclear DNA the bases are held together by hydrogen bonds. Nuclear DNA and mitochondrial DNA differ in many ways, starting with location and structure. Nuclear DNA is located within the nucleus of eukaryote cells and usually has two copies per cell while mitochondrial DNA is located in the mitochondria and contains 100-1,000 copies per cell. The structure of nuclear DNA chromosomes is linear with open ends and includes 46 chromosomes containing 3 billion nucleotides. Mitochondrial DNA chromosomes usually have closed, circular structures, and contain for example 16,569 nucleotides in human. Nuclear DNA is diploid, ordinarily inheriting the DNA from two parents, while
Extrachromosomal DNA that cell matures and expands, containing fully mature plastids. Extrachromosomal circular DNA (eccDNA) is present in all eukaryotic cells, is usually derived from genomic DNA, and consists of repetitive sequences of DNA found in both coding and non-coding regions of chromosomes. EccDNA can vary in size from less than 2000 base pairs to more than 20,000 base pairs. In plants, eccDNA contains repeated sequences similar to those that are found in the centromeric regions of the chromosomes and in repetitive satellite DNA. In animals, eccDNA molecules have been shown to contain repetitive sequences that are seen in satellite DNA, 5S