1. Nitrogenous base: This is a molecule with a nitrogen-containing ring structure. There are five main types of nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U).

2. Pentose sugar: This is a five-carbon sugar molecule. In DNA, the sugar is deoxyribose, while in RNA, the sugar is ribose.

3. Phosphate group: This is a molecule composed of phosphorus and oxygen.

These three parts are linked together to form a single nucleotide.