DNA forms: A, B, Z, H

One of the properties of the DNA is that it shows confirmational flexibility, and could exist in alternative structural forms. The Watson-Crick structure is the B-form DNA, or B-DNA. The B from is the most stable structure for a random sequence DNA molecule under physiological conditions and is therefore “the standard point of reference in any study of the properties of DNA” (Lehninger Principle of Biochemistry, Nelson and Cox, 2000, pp. 338). The B-DNA predominates in the cell. There are two other structural variants of DNA that have been well characterized in crystal structures. They are the A-DNA and Z-DNA. There is another alternative form of DNA known as the H-DNA. These DNA variants differ in their helical sense, diameter, base pairs per helical turn, helix rise per base pair, base tilt normal to the helix axis, sugar pucker conformation, and glycosyl bond conformation.