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Nucleic acids can adopt different conformations.

Geometrical features:

The distance between two subsequent base pairs along the helical axis is called helical rise (h).The pitch (p) is the length of the helix axis for one complete helix turn. The turn angle per nucleotide or twist angle (t) is given by 360° / number of nucleotides per turn. C2'-endo and C3'-endo are descriptions of sugar conformations.

The most frequently occurring nucleic acid model conformations are characterized by the following geometrical parameters :

These geometrical features lead to different widths and depths of the minor and major grooves of the nucleic acid double helix (data from Jeffrey, Saenger, Hydrogen Bonding in Biological Structures, Springer-Verlag, 1991, Table 20.1, p. 401).

Groove Width Groove Depth
Major Minor Major Minor
A-DNA 2.7 Å 11.0 Å 13.5 Å 2.8 Å
Z-DNA 11.7 Å 5.7 Å 8.5 Å 7.5 Å