1.2 RNA also consists of four different kinds of ribonucleotides 1.2.1 Each ribonucleotide unit is also made of three parts: a nitrogenous base, a pentose, and a phosphate group. 1.2.2 The base part is adenine, guanine, cytosine or uracil. 1.2.3 Uracil exists only in RNA, and thymine only in DNA1.2 RNA also consists of four different kinds of ribonucleotides. 1.2.1 Each ribonucleotide unit is also made of three parts: a nitrogenous base, a pentose, and a phosphate group. 1.2.2 The base part is adenine, guanine, cytosine or uracil. 1.2.3 Uracil exists only in RNA, and thymine only in DNA