Dna: A double-stranded polymer of four different monomers called nucleotides, namely adenosine, cytosine, guanosine, and thymidine. Besides other less significant forces, two forces stabilize the DNA in its natural state - hydrogen bonds between bases, and Van der Waals forces from stacking interactions between base pairs. There are three known forms of DNA, namely A-DNA, B-DNA and Z-DNA.