Nucleotide

(Nucleotide= nitrogenous base + pentose + phosphate)

(Download adenine.pdb, guanine.pdb, cytosine.pdb, uracil.pdb, thymine.pdb)

There are totally 2 types of purines (double ring) called adenine (A) and guanine (G), and also 3 types of pyrimidines (single ring) called cytosine (C), uracil (U) and thymine (T).

RNA is composed of ribonucleotides while DNA is composed of deoxyribonucleotides. You can identify them by the oxygen atom on the pentose (The one circled in black on the above graph). Ribonucleotides have 2 oxygen atoms attached to their pentose but deoxyribonucleotides have only ONE oxygen atom attached to their pentose.