This specificity results from the hydrogen-bonding
capacities of the bases themselves. Adenine and thymine form two
hydrogen bonds, and guanine and cytosine form three hydrogen
bonds. The specificity of molecular interactions within the DNA
molecule allows one to predict the sequence of nucleotides in one
polynucleotide strand if the sequence of nucleotides in the complementary
strand is known (24). Although the hydrogen bonds
themselves are relatively weak, the number of hydrogen bonds
within a DNA molecule results in a very stable molecule that
would never spontaneously separate under physiological conditions.
There are many possibilities for hydrogen-bonding between
pairs of heterocyclic bases. Most important are the hydrogenbonded
basepairs A:T and G:C that were proposed by Watson and
Crick in their double-helix structure of DNA (3,24). However,
other forms of base-pairing have been described (25,26). In addition,
hydrophobic interactions between the stacked bases in the
double helix lend additional stability to the DNA molecule.