We discuss the denaturation of long, double-stranded DNA pulled apart by a constant force. When the force approaches a critical threshold, a remarkable unzipping transition occurs which is strongly influenced by randomness in the base pair sequence. The DNA unzips via a series of discrete jumps and plateaus which allow it to reach successively deeper energy minima. Above the threshold force, the dynamics of unzipping is related to that of a particle diffusing in a random force field. Recently, the first observations of this striking behavior, carried out on several identical molecules in parallel, have been reported. The position and duration of the pauses in the separation are reproducible from molecule to molecule and depend on the applied force. For small forces, the DNA remains in a partially unzipped state. We expect similar energy landscapes together with anomalous drift and diffusion for certain molecular motors near the stall force.
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