Semiconservative replication describes the mechanism of DNA replication in all known cells. DNA replication occurs on multiple origins of replication along the DNA template strands. As the DNA double helix is unwound by helicase, replication occurs separately on each template strand in antiparallel directions. This process is known as semi-conservative replication because two copies of the original DNA molecule are produced, each copy conserving (replicating) the information from one half of the original DNA molecule.[1][2] Each copy contains one original strand and one newly synthesized strand. (Both copies should be identical, but this is not entirely assured.) The structure of DNA (as deciphered by James D. Watson and Francis Crick in 1953) suggested that each strand of the double helix would serve as a template for synthesis of a new strand. It was not known how newly synthesized strands combined with template strands to form two double helical DNA molecules.[3][4]