Final answer:
The correct order of base-pair strength from strongest to weakest is GC > AT > AU, due to GC pairs having three hydrogen bonds and AT or AU pairs having two.
Step-by-step explanation:
The correct order of base-pair strength in DNA/RNA from strongest to weakest is GC > AT > AU. This order is due to the number of hydrogen bonds that form between the base pairs. Adenine (A) pairs with thymine (T) in DNA or uracil (U) in RNA, forming two hydrogen bonds, while guanine (G) pairs with cytosine (C) creating three hydrogen bonds. The additional hydrogen bond gives GC base pairs more strength compared to AT or AU pairs.
Base pairing is crucial for the stability of the DNA double helix and plays a vital role in the preservation and transmission of genetic information. The pairing is guided by the structure of the nucleotide bases: adenine and guanine are purines, while cytosine and thymine (or uracil in RNA) are pyrimidines. The pairing of a purine with a pyrimidine ensures optimal spacing and hydrogen bonding, critical factors for the DNA's structural integrity.