Describe the double helix model of DNA with a labelled diagram

Explanation

The double helix model of DNA was explained by Watson and Helix.
DNA consists of two polynucleotide strands.
The polynucleotide strands are right hand coiled to form double helix.
Sugars and phosphates are the back box of the two strands.
Nitrogenous base is attached at right angles to the strand.
The nitrogenous bases are paired with hydrogen bonds. This is called base pairing
Adenine always pairs with thymine by two hydrogen bonds. Guanine always pairs with cytosine with by 3 hydrogen bonds.
The number of purines is equal to number of pyrimidines. This is called as Chargaff.s rule of base equivalence.