Explanation

DNA is a double helical molecule and it opens to form a replication fork for its replication. The two strands of DNA are joined with the help of H-bonds between the strands. Topoisomerases are specialised to cause nicks or breaks in the double helix and helps separate the DNA stands. Helicase unwinds the DNA helix from that nick caused by the topoisomerase and this separates the two strands. DNA gyrase introduces negative supercoils in DNA strands of prokaryotes. DNA polymerase adds nucleotide units to the 3′ end of a DNA chain. DNA ligase joins the ends of DNA.