A number of enzymes take role in the formation of DNA synthesis. Unwinding of DNA is done by:

A replication fork consists of four components that form in the following sequence: The DNA helicase unwinds a sho segment of the parental duplex DNA; A primase initiates synthesis of an RNA molecule that is essential for priming DNA synthesis; The DNA polymerase initiates nascent, daughter-strand synthesis; and Single-stranded DNA-binding proteins (SSBs) bind to ssDNA and prevent premature reannealing of ssDNA to dsDNA. Topoisomerases relieve torsional strain that results from helicase-induced unwinding. Must know: DNA ligase seals the single strand nick between the nascent chain and Okazaki fragments on lagging strand. Ref: Weil P. (2011). Chapter 35. DNA Organization, Replication, & Repair. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.