Chargaff

Avery s paper prompted other biochemists to rethink their ideas about DNA One of them Erwin Chargaff of Columbia University soon discovered that the distribution of adenine thymine cytosine and guanine differed from species to species but was the same within a species and within all the cells of a species Perhaps DNA did have the capacity to carry genetic information after all Chargaff also found that regardless of the source of the DNA half the bases were purines and the other half were pyrimidines Significantly the ratio of the purine adenine (A) to the pyrimidine thymine (T) was always close to 1 1 Likewise the ratio of the purine guanine (G) to the pyrimidine cyto sine (C) was also close to 1 1 For human DNA the values are... 

Avery s studies shed light on the function of DNA. Chargaff s touched on structure in that knowing the distribution of A, T, G, and C in DNA is analogous to knowing the fflnino acid composition of a protein, but not its sequence or three-dimensional shape. 

A clue to the chemical basis of base pairing in DNA came from the analysis of the base composition of various DNAs by Erwin Chargaff in the late 1940s. His data showed that the four bases commonly found in DNA (A, C, G, and T) do not occur in equimolar amounts and that the relative amounts of each vary from species to species (Table 11.3). Nevertheless, Chargaff noted that certain pairs of bases, namely, adenine and thymine, and guanine and cytosine, are... 

Molar Ratios Leading to the Formulation of Chargaff s Rules ... 

The Chemistry of Ribose and Deoxyribose, W. G. Overend and M. Stacey, Chapter 2 in The Nucleic Acids, Vol I. Chemistry and Biology, Edited by E. Chargaff and J. N. Davidson, Academic Press, (1955) 9- 80. 

C13-0102. hi the 1950s, Edwin Chargaff of Columbia University studied the composition of DNA from a variety of plants and animals. He found that the relative amounts of different bases changed from one species to another. However, in every species studied, the molar ratios of guanine to cytosine and of adenine to thymine were found to be very close to 1.0. Explain Chargaff s observations in terms of the Watson-Crick model of DNA structure. 

S. Zamenhof, Grace Leidy, Hattie E. Alexander, Patricia L. Fitzgerald and E. Chargaff, Arch. Biochem. and Biophys., 40, 50 (1952). 

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