Sugar phosphate backbone

A – DNA
When the relative humidity is lowered below roughly 75%, X-ray diffraction examinations of dehydrated DNA fibres showed a new form dubbed A – DNA.
1. A—DNA is a right-handed Double Helix made up of antiparallel strands kept together by Watson—Crick base pairing, similar to B—DNA.
2. The A Helix is longer and wider than the B helix, and its base pairs are bent instead of parallel to the helix axis.
3. The puckering of their ribose units causes a lot of the structural distinctions between them. C3 is out of the plane formed by the other four atoms of the furanose ring in A – DNA, while C2 is out of the plane in B – DNA. Furthermore, the minor groove almost vanishes.
4. The A Helix’s phosphate groups bind fewer H2O molecules than the phosphates in B –DNA. As a result, dehydration favours the A-type. Furthermore, the minor groove almost vanishes.
5. The A Helix’s phosphate groups bind fewer H2O molecules than the phosphates in B –DNA. As a result, dehydration favours the A-type.