A helicase protein moves rapidly on highly flexible single-stranded DNA track, using power provided by ATP hydrolysis. Once the helicase encounters a physical blockade that it cannot surmount, a conformational change in the helicase protein results in the recruitment of the initial site on the DNA, forming a loop. The helicase protein then snaps back to the beginning site on the DNA and repeats the movement. Repetitive movement on the DNA may keep it clear of potentially toxic proteins.

Animation: Courtesy of Taekjip Ha