DNA replication requires several key enzymes to unwind, unwind, and synthesize a new double strand of DNA. Helicase unwinds the double helix by breaking hydrogen bonds. Topoisomerase breaks phosphodiester bonds ahead of the replication fork to prevent overwinding of DNA. Primase synthesizes RNA primers providing a 3' end for DNA polymerase to bind and add new nucleotides, forming new phosphodiester bonds through dehydration synthesis and replacing RNA primers with DNA. Ligase seals together the breaks in DNA between Okazaki fragments.