These nitrogenous bases are adenine (A), uracil (U), guanine (G), thymine (T), and cytosine (C). These nitrogenous bases hydrogen bond between opposing DNA strands to form the rungs of the twisted ladder or double helix of DNA or a biological catalyst that is found in the nucleotides.Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as base pairs.hese nitrogenous bases hydrogen bond between opposing DNA strands to form the rungs of the twisted ladder or double helix of DNA or a biological catalyst that is found in the nucleotides. Adenine is always paired with thymine, and guanine is always paired with cytosine. These are known as base pairs.