(1) there are two strands which run antiparallel one in 5' $ \rightarrow $ 3' direction and other in 3' $ \rightarrow $ 5'
(2) the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
(3) there are two strands which run parallel in the 5' $ \rightarrow $ 3' direction
(4) the proportion of Adenine in relation to thymine varies with the organism
