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$DNA$ is the chemical name for the molecule that carries the genetic information of all living beings.
The polymer molecule consists of $2$ strands that wind around each other to create a form called a spiral. Every strand includes
a backbone manufactured from alternating sugar (deoxyribose) and phosphate molecules.
The two polynucleotide chains or strands of polymer are joined up by Hbonding.
Adenine-Thymine ( has two $H-$bonds) and Cytosine-Guanine (has three $H-$bonds).
Therefore the double-helical structure of $DNA$ is due to $H$-bonding.
