DNA or deoxyribose nucleic acid is the largest macromolecule made of the helically twisted two antiparallel polydeoxyribonucleotide strands held together by hydrogen bonds. The two strands of DNA are together called DNA duplex. It has a diameter of 20Å. One turn spiral has a distance of 34Å. It contains 10 deoxyribonucleotides in each strand so that the distance between two adjacent nucleotides is 3.4Å.