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Purines (adenine and guanine) are larger, double-ring nitrogenous bases found in DNA and RNA, while pyramidines (cytosine, thymine, and uracil) are smaller, single-ring bases. Purines always pair with pyramidines in DNA strands to maintain the proper structure of the double helix.
i) thymine ii) cytosine and iii) - in Rna only is found - uracil.
Saturn has many colorful rings.
how many rings does mars have
Venus does not have rings.
mercury has no rings
6 rings
2 rings
You question dosent really make sence, but if you are asking why are they not Purines and Pyramidines...They are Adenine and Guanine are Purines, and then you can realise that Thymine Cytosine and Uracil are all Pyramidines. If you are asking why are they only considered as purines and prymidines they are not there a many different types of Purines and Pyramidines but because when you study Biology and DNA is a topic that you cover frequently, they are noted but an example of a Purine is Uric Acid (essentially a product when it a Purine is broken down but still considered as a Purine). Hope this is helpful...
4 Superbowl rings.
There are no rings in Venus.
it has 13 rings