Question

Why purine : pyrimidine ratio is 1:1 in DNA while it is not so in RNA?

Answer 1

In DNA complementary base pairing exists,I.e., purines always form bonds with pyrimidines.

(Number of adenine is always equal to number of thymine and number of guanine is equal to number of cytosine)

RNA, being single stranded has no complementary base pairing.

Hence, ratio of pyrimidines:purines in DNA is 1:1 and not so in rna.

Cheers!

Answer 2

The purine: pyrimidine ratio is 1:1 in DNA while it is not so in RNA because in RNA the base pairing is not fixed and definite.

Explanation:

In DNA there are four bases present namely Adenine, Guanine, Thymine and Cytosine. These base pairs are complementary to each other and Adenine pairs with Thymine with double bond and Guanine pairs with cytosine with triple bond. This kind of base pairing gives 1:1 ratio in DNA.

But this is not possible in case of RNA because for most of the species it is single stranded.