Supercoiled

Localised unwinding of a circular DNA molecule, which occurs during DNA replication, induces torsional stress into the remaining portion of the molecule because the ends of the strands are not free to rotate. As a result, the DNA molecule twists back on itself, like a twisted rubber band, forming supercoils.[1]

References

1. ^ Lodish,H.,Berk,A.,Kaiser,C.A.,Krieger,M.,Bretscher,A.,Ploegh,H., and Amon,A. (2013) Molecular Cell Biology,7th Edition, International Edition.