ABSTRACT
A left-handed helix (molecular structure) of DNA, in contrast to A-DNA and B-DNA that are right-handed helix structures. The difference is in the direction of the double-helix twist (Z-DNA is an alternative form of B-DNA in which the double helix unwinds to the left instead of the right). Z-DNA has the most base pairs per turn (in the helix) and so has the least twisted structure; it is very “skinny” and its name is taken from the zigzag path that the sugar-phosphate “backbone” follows along the helix. This is quite different from the smoothly curving path of the backbone of B-DNA. The Z-form of DNA has been found in polymers that have an alternating purinepyrimidine sequence.
