In the DNA molecule:

there are two strands which run antiparallel-one in $\displaystyle 5^{\prime} \rightarrow 3^{\prime}$ direction and other in $\displaystyle 3^{\prime} \rightarrow 5^{\prime}$

the total amount of purine nucleotides and pyrimidine nucleotides is not always equal

there are two strands which run parallel in the $\displaystyle 5^{\prime} \rightarrow 3^{\prime}$ direction

the proportion of Adenine in relation to thymine varies with the organism