Helicases adopt different structures and [[oligomerization]] states. Whereas [[dnaB helicase|DnaB]]-like helicases unwind [[DNA]] as donut-shaped [[hexamer]]s, other enzymes have been shown to be active as [[monomer]]s or [[protein dimer|dimer]]s. Studies have shown that helicases may act passively, waiting for uncatalyzed unwinding to take place and then translocating between displaced strands,<ref name=Croquette>{{cite journal |author=Lionnet T, Spiering MM, Benkovic SJ, Bensimon D, Croquette V|title=Real-time observation of bacteriophage T4 gp41 helicase reveals an unwinding mechanism |journal=PNAS |volume=104 |issue=50 |pages=19790–19795 |year=2007 |pmid=18077411 |doi=10.1073/pnas.0709793104 |pmc=2148377}}</ref> or can play an active role in catalyzing strand separation using the energy generated in ATP hydrolysis.<ref name=Johnson>{{cite journal |author=Johnson DS, Bai L, Smith BY, Patel SS, Wang MD |title=Single-molecule studies reveal dynamics of DNA unwinding by the ring-shaped t7 helicase |journal=Cell |volume=129 |issue=7 |pages=1299–309 |year=2007 |pmid=17604719 |doi=10.1016/j.cell.2007.04.038 |pmc=2699903}}</ref> In the latter case, the helicase acts comparably to an active motor, unwinding and translocating along its substrate as a direct result of its ATPase activity.<ref name=physorg1>{{cite web |url=http://www.physorg.com/news102663442.html |title=Researchers solve mystery of how DNA strands separate |date=2007-07-03 |accessdate=2007-07-05}}</ref> Helicases may process much faster ''[[in vivo]]'' than ''[[in vitro]]'' due to the presence of accessory proteins that aid in the destabilization of the fork junction.<ref name=physorg1 />
