Why is chargaff's rule important to DNA?

Chargaff's rule states that DNA from any cell of any organism has a 1:1 ratio of pyrimidine and purine bases and, more specifically, that the amount of guanine, a purine base, is equal to cytosine, a pyrimidine base; and the amount of adenine, a purine base, is equal to thymine, a pyrimidine base.

So a base pair is composed of a pyrimidine base and a purine base. This pattern is found in both strands of DNA, and is responsible for the base-pairing rule, which states that adenine always pairs with thymine, and guanine always pairs with cytosine..


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http://www.bio.miami.edu/~cmallery/150/gene/c16x6base-pairs.jpg. Branched DNA

The nitrogen bases pair with each other by means of hydrogen bonds.