Nitrogenous bases are adenine, guanine, cytosine, and thymine in DNA. One of the chemical differences between DNA and RNA is that in RNA, the nitrogenous base uracil is used instead of thymine. Nitrogenous bases can form hydrogen bonds. Adenine, thymine, and uracil can form two hydrogen bonds. Guanine and cytosine can form three hydrogen bonds. In nucleic acids (DNA and RNA), nitrogenous bases can bind to each other by hydrogen bonding. Guanine binds to cytosine, and cytosine binds to guanine. In DNA, adenine binds to thymine. In RNA, adenine binds to uracil.