Structural Parameters of DNA
| DNA form | A (Anhydrous) | B (Biological) | Z (Zig-zag) |
| Occurrence | DNA:RNA
RNA:RNA |
Major form in vivo | High salt form
Py-pu sequences |
| Helical rotation | Right | Right | Left |
| Diameter (Å) | 23 | 20-22 | 18 |
| Bp/turn | 11+ | 10+ | 12 (6 py-pu dimers) |
| Pitch/helical turn (Å) | 28 | 33.2 | 44.6 |
| Helical rise/bp (Å) | 2.6-3.3 | 3.0-3.4 | 7.4b |
| Rotation per base (°) | 32.7 | 36 | -60b |
| Major groove (depth x width)(Å) | 13.5 x 2.7 | 8.5 x 11.7 | nil |
| Minor groove (depth x width)(Å) | 2.8 x 11 | 7.5 x 5.7 | Narrow and deep |
| Base tilt relative to helical axis (°) | High,10 to 20 | Low = -1.2 | -7 |
| Mean Propeller twist (°) | 18 | 16 | c.a. 0 |
| Displacement relative to helical axis (Å) | 4.4 - 4.9c | ~ 0 | -4 |
| Glycosyl bond conformation relative to minor groove | Anti | Anti | Py = anti ; pu = syn |
| Sugar pucker | C3'-endo | C2'-endo | Py = C2' -endo Pu = C3' -endo |
| Distance between adjacent phosphates (Å) | 5.9 | 7.0 | 5.7 - 7.3 |
a: cf Dickerson 1992 and Saenger 1984
b: Values for dinucleotide repeats
c: resulting in an open central cylinder of 3 to 5 Å