DNA is found in nearly all living cells. However, its exact location within a cell depends on whether that cell possesses a special membrane-bound organelle called a nucleus. Organisms composed of cells that contain nuclei are classified as eukaryotes, whereas organisms composed of cells that lack nuclei are classified as prokaryotes. In eukaryotes, DNA is housed within the nucleus, but in prokaryotes, DNA is located directly within the cellular cytoplasm, as there is no nucleus available.