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In cells, DNA is constantly twisted, bent and stretched by numerous proteins mediating genome transactions. Understanding these essential biological processes requires in-depth knowledge of how DNA complies to mechanical stress. Two important physical features of DNA, helical structure and sequence, are not incorporated in current descriptions of DNA elasticity. Here we connect well-defined force–extension measurements with a new model for DNA elasticity: the twistable worm-like chain, in which DNA is considered a helical, elastic entity that complies to tension by extending and twisting. In addition, we reveal hitherto unnoticed stick–slip dynamics during DNA overstretching at ∼65 pN, caused by the loss of base-pairing interactions. An equilibrium thermodynamic model solely based on DNA sequence and elasticity is presented, which captures the full complexity of this transition. These results offer deep …