Features of DNA structure:

1. DNA exists as a double helix in which the two polynucleotide chains are coiled about one another in a spiral with a diameter of about 20Å.

2. Concentration of thymine was always equal to the concentration of adenine and the concentration of cytosine was always equal to the concentration of guanine.

3. Each polynucleotide chain consists of a sequence of nucleotides linked together by phosphodiester bonds, joining adjacent deoxyribose moieties

4. The two polynucleotide strands are held together in their helical configuration by hydrogen bonding.

5. The two polynucleotide chains generally exist in perpendicular to the axis of the molecule like the spiral staircase.

6. The bases of one polynucleotide chain pairs with the bases of other polynu­cleotide chain. These pairing always con­sist of one purine with one pyrimidine. In a strict sense, the base pairing is fixed and specific, e.g. adenine is always paired with thymine and guanine with cytosine.