Chargaff's Rule
In the late 1940s, Chargaff formulated a fundamental principle that describes the specific base pairing in DNA. It consists of two main components:
☛ Total amount of purine is equal to the total amount of pyrimidines.
i.e. G + A = T + C
☛ Amount of Adenine (A) is equal to the amount of Thymine (T) and the amount of Guanine (G) is equal to the amount of cytosine (C)
i.e. A = T
G = C
☛The ratio of (A + T) / (G + C) is constant for a species (human being 1.55, pea 1.62, Euglena 0.88, E. coli 0.93, etc.). This ratio (A + T) / (G + C) is not equal to one.
☛ Sugar deoxyribose and phosphate occurs in equimolar proportion.
☛ The nucleotide in the helix are joined together by phosphodiester bonds. Sugar and phosphate molecules from the backbone of the DNA strand.
☛ The sugar and phosphate backbone do not conceal the bases inside. There are two groove along the surface of the DNA molecule. One is wide and deep is called minor groove and other is narrow and shallow is called minor groove.
The base composition of DNA from various organisms are listed below in the table. Data from this table supports both of Chargaff's rules.
| Organism | %A | %G | %C | %T | A/T | G/C | %GC | %AT |
|---|---|---|---|---|---|---|---|---|
| E. coli | 24.7 | 26.0 | 25.7 | 23.6 | 1.05 | 1.01 | 51.7 | 48.3 |
| Yeast | 31.3 | 18.7 | 17.1 | 32.9 | 0.95 | 1.09 | 35.8 | 64.4 |
| Maize | 26.8 | 22.8 | 23.2 | 27.2 | 0.99 | 0.98 | 46.1 | 54.0 |
| Wheat | 27.3 | 22.7 | 22.8 | 27.1 | 1.01 | 1.00 | 45.5 | 54.4 |
| Grasshopper | 29.3 | 20.5 | 20.7 | 29.3 | 1.00 | 0.99 | 41.2 | 58.6 |
| Sea Urchin | 32.8 | 17.7 | 17.3 | 32.1 | 1.02 | 1.02 | 35.0 | 64.9 |
| Octopus | 33.2 | 17.6 | 17.6 | 31.6 | 1.05 | 1.00 | 35.2 | 64.8 |
| Chicken | 28.0 | 22.0 | 21.6 | 28.4 | 0.99 | 1.02 | 43.7 | 56.4 |
| Rat | 28.6 | 21.4 | 20.5 | 28.4 | 1.01 | 1.00 | 42.9 | 57.0 |
| Human | 29.3 | 20.7 | 20.0 | 30.0 | 0.98 | 1.04 | 40.7 | 59.3 |
Which of the following is correct
A. The amount of adenine and guanine is equal to the amount of uracil and cytosine
B. The amount of adenine and uracil is equal to the amount of guanine and cytosine
C. The amount of adenine and thymine is equal to the amount of guanine and cytosine
D. The amount of adenine and guanine is equal to the amount of thymine and cytosine
