Chargaff's Rule

The Chargaff's rule calculator finds the percentage and number of every nucleotide in a DNA molecule from one known nucleotide, as well as the DNA length, mass and the number of hydrogen bonds.

Chargaff's rule

In double-stranded DNA adenine sits opposite thymine and guanine opposite cytosine, so:

A = T, G = C, A + G = T + C = 50%

Knowing the share of one nucleotide, its complement has the same share, and the other pair gets 100% − 2 · p, split equally.

Example. A DNA molecule has 880 guanine nucleotides, 22% of the total. Then C = 22% and A = T = (100 − 44) / 2 = 28%. There are 880 / 0.22 = 4000 nucleotides in total: 1120 each of adenine and thymine and 880 of cytosine.

DNA length and mass

• The number of base pairs is half the number of nucleotides; DNA length = pairs · 0.34 nm.
• DNA mass = number of nucleotides · 345 Da.
• Hydrogen bonds: 2 for each A — T pair and 3 for each G — C pair.