Definition for Z-DNA
From Biology Forums Dictionary
1) Z-DNA is one of the many possible double helical structures of DNA. It is a left-handed double helical structure in which the double helix winds to the left in a zig-zag pattern (instead of to the right, like the more common B-DNA form). Z-DNA is thought to be one of three biologically active double helical structures along with A- and B-DNA.
2) This is a structure of antiparallel chains that twist in a left-handed screw. The phosphates are zigzagged. It is the narrowest helix, with a long rise, increased bases per turn, and large pitch. The major groove is flatter, and the minor groove is very deep.