Describe the double helix structure of $DNA$ and explain how the sequences of the other strand are predicted.

(N/A) The base pairing confers a very unique property to the polynucleotide chains.
They are said to be complementary to each other,and therefore,if the sequence of bases in one strand is known,then the sequence in the other strand can be predicted.
Also,if each strand from $DNA$ acts as a template for the synthesis of a new strand,the two double-stranded $DNA$ (daughter $DNA$) molecules thus produced would be identical to the parental $DNA$ molecule. Because of this,the genetic implications of the structure of $DNA$ become very clear.
The salient features of the double helix structure of $DNA$ are as follows:
$(i)$ It is made of two polynucleotide chains where the backbone is constituted by sugar-phosphate and bases project inside.
$(ii)$ The two chains have anti-parallel polarity. It means,if one chain has the polarity $5^{\prime} \rightarrow 3^{\prime}$,the other has $3^{\prime} \rightarrow 5^{\prime}$.
$(iii)$ The bases in two strands are paired through hydrogen bonds ($H$-bonds) forming base pairs $[bp]$. Adenine $(A)$ forms two hydrogen bonds with Thymine $(T)$ from the opposite strand and vice-versa,while Guanine $(G)$ forms three hydrogen bonds with Cytosine $(C)$ and vice-versa.