DNA Structure and Replication

ID #1065

Is there a specific reason why there are 2 bonds between A and T, and 3 bonds between G and C, or is it just due to their structures? Do the number of bonds have any significance besides A-T being easier to break?

No, the only specific reason is the three-dimensionality of the chemical groups. For a hydrogen bond to form, you have to have a partially positive atom near a positively negative atom. This only "fits" with A-T and G-C base pairs -- the other potential pairings result in two partially negative atoms too near each other or something similar. And also, the relative energy needed to break a G-C pair versus an A-T pair is the significance of the number of bonds. It might sound simple, but this difference is exploited to the cell's advantage over and over.

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