Each compound that makes up the bases of the DNA can only be paired with a certain other base. Adenine and Guanine are called pyrimidines and are smaller in size compared to Cytosine and Guanine, which are called purines. Pyrmidines are more diminutive than pyrimidines because of their combination of six/five cornered rings, whereas purines are molecules made up of only six cornered rings. So, one pyrimidine and one purine will be paired together to get the right size needed to fit between the two strands of DNA, because two purines or two pyrimidines bonded together will either be too small or too large to fit in between the two DNA strands. So, because of this, Adenine will ALWAYS be paired with Thymine, and Cytosine will ALWAYS be paired with Guanine, and therefore there will also be the same amount of Adenine as there are Thymine and Cytosine as there is Guanine.
These bases, along with their pairs, are held together with a weak hydrogen bond. Since the bond joining a pair of two bases is not very strong, the DNA double helix can be easily separated into two with minimal energy, for easy access the information withheld inside.
Also: The different patterns or combinations of the order in which the paired bases are in, decide the genetic makeup of the inheriting organism.
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were fully composed, as well as altered images and diagrams, by Josh Eisma (2002), unless otherwise specified.
