Principles of Biochemistry Volume 3 - A. Lehninger 1985
Molecular Mechanisms of Genetic Information Transmission
DNA: Structure of Chromosomes and Genes
DNA from different species has a distinct nucleotide composition
The most crucial clue to unravelling The Structure of DNA was the discovery made in the late 1940s by Erwin Chargaff and his colleagues at Columbia University. They found that the four bases occur in the DNA of different organisms in varying proportions and that a definite quantitative relationship exists among them. Table 27-3 presents the quantitative ratios of the four bases (A, T, G, and C) in DNA preparations isolated from various living species. Results of this kind, obtained for DNA preparations isolated from a vast array of different species, led Chargaff and later researchers to the following Conclusions:
1. DNA preparations isolated from different Tissues of the same species have the same nucleotide composition.
Class="center">Table 27-3. Base Ratios in DNA1)
|
Nucleotide composition, mol % |
Base ratios |
||||||
A |
G |
C |
T |
A/T |
G/C |
||
Human |
30,9 |
19.9 |
19,8 |
29,4 |
1,05 |
1,00 |
1,04 |
Sheep |
29,3 |
21,4 |
21,0 |
28,3 |
1,03 |
1,02 |
1,03 |
Chicken |
28,8 |
20,5 |
21,5 |
29,3 |
1,02 |
0,95 |
0,97 |
Turtle |
29,7 |
22,0 |
21,3 |
27,9 |
1,05 |
1,03 |
1,05 |
Salmon |
29,7 |
20,8 |
20,4 |
29,1 |
1,02 |
1,02 |
1,02 |
Sea urchin |
32,8 |
17,7 |
17,3 |
32,1 |
1,02 |
1,02 |
1,02 |
Locust |
29,3 |
20,5 |
20,7 |
29,3 |
1,00 |
1,00 |
1,00 |
Wheat germ |
27,3 |
22,7 |
22,8 |
27,1 |
1,01 |
1,00 |
1,00 |
31,3 |
18,7 |
17,1 |
32,9 |
0,95 |
1,09 |
1,00 |
|
E. coli |
24,7 |
26,0 |
25,7 |
23,6 |
1,04 |
1,01 |
1,03 |
Staphylococcus aureus |
30,8 |
21,0 |
19,0 |
29,2 |
1,05 |
1,11 |
1,07 |
Phage T7 |
26,0 |
24,0 |
24,0 |
26,0 |
1,00 |
1,00 |
1,00 |
Phage λ |
21,3 |
28,6 |
27,2 |
22,9 |
0,92 |
1,05 |
1,00 |
Phage φX174 (replicative form) |
26,3 |
22,3 |
22,3 |
26,4 |
1,00 |
1,00 |
1,00 |
1) Note that the nucleotide compositions of human and S. aureus DNA are nearly identical. Each species has a characteristic DNA nucleotide composition, and differences in nucleotide composition among different species can sometimes be very subtle.
2. The Nucleotide Composition of DNA varies from one species to another.
3. The nucleotide composition of DNA in a given species does not change with the organism's age, nor is it affected by its diet or environmental changes.
4. In any DNA, regardless of the species, the number of adenine residues equals the number of thymine residues (i.e., A = T), and the number of guanine residues always equals the number of cytosine residues (G = C). It follows from these relationships that the sum of purine residues equals the sum of pyrimidine residues, i.e., A + G = T + C.
These quantitative relationships, later confirmed by many researchers, not only served as an essential prerequisite for determining the three-dimensional structure of DNA, but also helped to understand how Genetic information is encoded in DNA and transmitted from one generation to the next.
Last update: 06/08/2026
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