Scientists from the California Institute of Technology have fabricated a motor that runs autonomously, and is powered only by the free energy of DNA hybridization. The molecular motor was inspired by bacterial pathogens such as Rickettsia rickettsii that propel themselves through host cells by polymerizing protein “comet tails.” The synthetic mimic operates by polymerizing a double-helical DNA tail out of metastable DNA hairpins (a pattern named for its 180-degree turn).