AP BIOLOGY

Detailed explanation-1: -Chargaff’s realization that A = T and C = G, combined with some crucially important X-ray crystallography work by English researchers Rosalind Franklin and Maurice Wilkins, contributed to Watson and Crick’s derivation of the three-dimensional, double-helical model for the structure of DNA.

Detailed explanation-2: -The biochemist Erwin Chargaff had found that while the amount of DNA and of its four types of bases–the purine bases adenine (A) and guanine (G), and the pyrimidine bases cytosine (C) and thymine(T)–varied widely from species to species, A and T always appeared in ratios of one-to-one, as did G and C.

Detailed explanation-3: -Further a 1:1 stoichiometric ratio of purine and pyrimidine bases (i.e., A+G=T+C ) should exist. This pattern is found in both strands of the DNA. They were discovered by Austrian-born chemist Erwin Chargaff, in the late 1940s.

Detailed explanation-4: -(1949) Erwin Chargaff studied the nitrogenous bases; discovered the base-pairing rules that the amount of adenine (A) equals the amount of thymine (T) and the amount of cytosine (C) equals the amount of guanine (G); A=T and C=G!

Detailed explanation-5: -This sentence refers to the work of Erwin Chargaff, a biochemist at Columbia University. In the late 1940s, Chargaff analyzed the proportions of the four different types of base molecules in DNA, and found that DNA always contains equal amounts of guanine and cytosine, and equal amounts of adenine and thymine.