Sugar-phosphate backbone is linked tophosphodiester bond between carbon 4 and CH2 group that attached to phosphate ion thus make the DNA strand as double helix making it twist into a coil. The reason of this coiling structure is in order to protect the bases inside it protecting from being damaged from the environment and each turn of this helix is 34nm long in which 10 bases attached per turn.
Sugar-phosphate backbone produces energy minima matching by simple replacement of bases such as cytosine, guanine, adenine and thymine which shows mutual base position characteristic of the target sequence and it demonstrates one major degree of freedom consisting of torsion angles chi, delta, zeta and pseudorotation phase angle. The stacking interaction shows side-roll-twist, shift-tilt and rise which is more or less constant.
Sugar-phosphate backbone is composed of alternating sugar and phosphate that defines directionality of the molecules which is negatively charged and hydrophilic to allow the DNA backbone to form bonds with water. Mutagens damaged the DNA strand which leads to change in normal sequencing including base modification and double-strand breaks which is difficult to repair, as a results it eventually produced point mutations, insertions and deletion of DNA sequence.