The code of life breaks the local two-fold rotation symmetry of the DNA double helix. While the sense strand codes for mRNA during transcription, the complementary strand does not. Yet, at the start of replication, base pairs must break the bonds that lock in the code. In the sudden approximation, the chance that the split pair lands in the excited enol-imino tautomeric states rather than the dominant keto-amino form goes as the square of the super-exchange amplitude for protons to swap between bases. We estimate this amplitude using the tight-binding approximation of the proton wavefunction. The resulting exchange splitting gives an electric quadrupole transition which can be probed with coherent two-photon spectroscopy in the sub-millimeter regime. When the excited tautomers pair with dominant forms, proton swaps between bases restore the symmetry between strands and provide the mechanism for mutation.

Proton swaps between bases: Mechanism for mutation

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