State the physical structure of $DNA$.

(N/A) $DNA$ is a long polymer of deoxyribonucleotides.
$\Rightarrow$ The length of $DNA$ is usually defined as the number of nucleotides (or a pair of nucleotides referred to as base pairs) present in it.
This is also a characteristic feature of an organism.
For example,a bacteriophage known as $\phi \times 174$ has $5386$ nucleotides,Bacteriophage lambda has $48502$ base pairs $(bp)$,Escherichia coli has $4.6 \times 10^{6} \ bp$,and the haploid content of human $DNA$ is $3.3 \times 10^{9} \ bp$.