Final answer:
Chargaff's rule states the amount of adenine equals the amount of thymine, and the amount of cytosine equals the amount of guanine in double-stranded DNA. These base pairings are consistent across species and essential for DNA structure and replication.
Step-by-step explanation:
Chargaff's rule states that, "in a piece of double-stranded DNA, the amount of adenine equals the amount of thymine and the amount of cytosine equals the amount of guanine." This is a foundational concept in molecular biology that reflects the base-pairing rules of DNA's structure. In short, the bases adenine (A) and thymine (T) pair together, and the bases cytosine (C) and guanine (G) pair together. These base pairs are held together by hydrogen bonds in the double helix of DNA, with adenine and thymine connecting by two hydrogen bonds and cytosine and guanine connecting by three hydrogen bonds.
The findings of Erwin Chargaff played a crucial role in the discovery of the DNA double helix structure by James Watson and Francis Crick. They indicated that these base pairing rules are consistent across different species, emphasizing that within a species, the ratios of A to T and G to C are constant, which has been immensely useful in understanding genetics and the process of DNA replication.