Helicase
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Helicase is an enzyme vital to all living organisms. Its function is to temporarily separate the two strands of a DNA double helix so that DNA or RNA synthesis can take place. RNA polymerase has its own helicase activity, whereas in DNA polymerase the helicase is a separate subunit.
Helicase subunit in DNA polymerase is a donut-shaped enzyme and is produced by the DnaB gene. In conjunction with DNA primase helicase promotes DNA unwinding by binding to the initiator proteins and loading into the DNA. Helicase then denatures (untwists) the DNA by hydrolysis of adenosine triphosphate (ATP). Continuous hydrolysis of ATP allows helicase to move along the single strand of DNA, untwisting double-stranded DNA that it encounters. An enzyme topoisomerase binds to the double-stranded DNA downstream of the unwound DNA to prevent excess strain on the helix.
Helicase is a necessary enzyme for eukaryote DNA because DNA polymerase requires a single-stranded DNA as a template in order to replicate DNA.