In the DNA molecule, four types of nitrogenous bases are found: cytosine (C), and guanine (G), adenine (A) and thymine (T). In DNA the bases pair up with each other in the following ways: A pairs with T by two hydrogen bonds, while C pairs with G by three hydrogen bonds. In RNA (i.e., transcript sequence), T is replaced by uracil (U). Moreover, the RNA nucleotide sequence is read in the direction 5' to 3'.