DNA replication is a complex and multi step process, which require enzymes, protein and metal ions. In eukaryotes the replication of DNA occurs in the S phase of cell cycle and it takes place in the nucleoplasm. In prokaryotes, replication occurs in the nucleus. It takes place before the cell division. Nucleoid is a made up of DNA molecule. It can be linear or circular. In virus, nucleic acid can be DNA or RNA.