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
Neuronal cell cycle neurons, which are able to replicate their DNA without neuronal death (Smith et al., 2000). Neurons that are Rb deficient have also been found to re-enter the cell cycle and survive in a 4C DNA state (Lipinski et al., 2001). Duplication of DNA can lead to neuronal diversification in vertebrates, as seen in observations in the developing chick retina. These neurons re-enter the cell cycle as they travel to the ganglion cell layer when they are activated by p75NTR. These neurons are unable to enter mitosis and are stuck in a 4C DNA content state. Cell cycle re-entry by p75NTR