According to Watson and Crick model of DNA, the DNA molecule is made up of two helical DNA chains that are wound around the same axis. The hydrophilic backbones of alternating sugar and phosphate groups are present on the outside of the double helix facing the surrounding water. Each nucleotide base of one strand is paired in the same plane with a base of the other strand. The distance between two consecutive base pairs is 0.34 nm and one complete turn of the double helix has 10 base pairs which means that it is 3.4 nm/ 34Å long