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In the DNA molecule
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- the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
- there are two strands which run parallel in the 5′ → 3′ direction
- the proportion of Adenine in relation to thymine varies with the organism
- there are two strands which run anti parallel one in 5′ → 3′ direction and other in 3′ → 5′
Correct Option: D
In the DNA molecule, there are two strands which run anti parallel one is 5' - 3' direction and other in 3' -5' direction, the two chains are held together by hydrogen bonds between their bases. Adenine (A), a purine of one chain his exactly opposite thymine (T), a pyramidine of the other chain. Similarly, cytosine (C), a pyrimidine lies opposite guanine (G), a purine. This allows a sort of lock & key arrangment between large sized purine & small sized pyrimidine. It is strengthened by the appearance of hydrogen bonds between the two.
