The DNA (deoxyribonucleic acid) is the double helical in structure. It has two anti parallel strands of long polynucleotides. The nucleotides are two purines ( adenine and guanine) and two pyrimidines ( thymine and cytosine). These purines and pyrimidines are attached with their complementary. Adenine pairs with the thymine with the two hydrogen bonds and the guanine pair with cytosine by three hydrogen bonds. The two strands are twisted which is responsible for the helical structure. The overall charge on the DNA molecule is the negative charge.