a | By stretching a double-stranded DNA (dsDNA) molecule, RNA polymerase (RNAP) is tracked in real time and stalled under an applied load148. t1, t2 and t3 represent three successive time points as the bead is pulled from the trap centre. b | By unzipping a dsDNA molecule, RNAP, which is trailed by another motor, Mfd, is tracked in real time169. c | By twisting two dsDNA molecules via a combination of optical tweezers and a micropipette, a DNA braid is formed and used to study topoisomerase relaxation174. d | By combining fluorescence detection and force manipulation, the replicative helicase CMG is observed to dynamically transition between single-stranded DNA (ssDNA) and dsDNA178.