Q. Which kind of chemical bond maintains the pairing of each chain in the DNA molecule?
To form the DNA molecule, purine bases bind to pyrimidine bases by intermolecular bonds known as hydrogen bonds. Hydrogen bonds occur when there is hydrogen near one of these electronegative elements: fluorine, nitrogen or oxygen.
In such conditions hydrogen looks like having lost electrons for those elements and an extremely strong polarization is created. The highly positive hydrogen attracts pairs of electrons of other molecules making a hydrogen bond.