DNA is composed of four nucleotides, each containing: adenine, cytosine, thymine, or guanine.
The amounts of A = T, G = C, and purines = pyrimidines [Chargaff's Rule].
DNA is a double-stranded helix with antiparallel strands [Watson and Crick].
Nucleotides in each strand are linked by 5'-3' phosphodiester bonds
Bases on opposite strands are linked by hydrogen bonding: A with T, and G with C.