z-dnahttp://www.oed.com/dictionary/z-dna_n%3Ftab%3Dmeaning_and_useZ-DNA, n.
First published 1986; not fully revised

Z-DNAnoun

Biochemistry.
  1. 1979–
    DNA in which the double helix has a left-handed rather than the usual right-handed twist and the sugar phosphate backbone follows a zigzagged course.
    1. 1979
      In looking at this left-handed helix..it is apparent that the ribose-phosphate backbone follows a zig-zag course resulting from alternating residue conformations. Accordingly, we propose to call this Z-DNA.
      A. H.-J. Wang et al. in Nature 13 December 681/2
    2. 1983
      In Z DNA..the repeating unit of the helix is not a single base pair, as it is in A and B DNA, but rather two successive base pairs: G–C followed by C–G.
      Scientific American December 92/1

Originally published as part of the entry for Z, n.

Z, n. was first published in 1921; not fully revised.