Final answer:
In DNA, GC and AT are the only permissible base pairs due to specific hydrogen bonding and the need to maintain the DNA's structural integrity with a uniform diameter, ensuring the accuracy of genetic information replication.
Step-by-step explanation:
In the structure of DNA, GC and AT pairings are the only base pairs allowed in the double helix due to specific hydrogen bonding rules and molecular sizes. Guanine (G) and cytosine (C) form three hydrogen bonds, while adenine (A) and thymine (T) form two. This is an outcome of the molecular structures where purines (A and G) always pair with pyrimidines (T and C) to maintain a uniform helical structure. Chargaff's rules supported this observation, as the A/T and G/C ratios in DNA molecules are constant for each species, suggesting that A pairs exclusively with T, and G with C.
The stable hydrogen bonding and specific pairings contribute to the replication accuracy of DNA during cell division. Additionally, the uniform diameter of the double helix enhances the electrostatic interactions holding the strands together, ensuring the stability of the genetic material.
The purine-pyrimidine pairing ensures not only the structural integrity of the DNA molecule with a uniform diameter but also the perfect match during replication. This complementary base pairing is fundamental to the preservation of genetic information across generations.