Pyrimidines Purihes NH. NH CH U CH Cytosine Thymine Uracil Adenine Guanine Ph sphate Nitrogenous base Pentose sugar HO 0 Ribose (in RNA) Doxyribose (in DNA) Pyrimidines Cytosine Thymine Uracil C T U Purihes Adenine Guanine A G Nitrogenous base Phosphate Pentose sugar HOCH2 HO OH Ribose (in RNA) HOCH2 H OH Doxyribose (in DNA)