1. Phosphate group: This is a negatively charged group that gives nucleotides their acidic properties. It is also important for the energy storage and transfer functions of nucleotides.

2. Sugar group: This is a five-carbon sugar, either ribose (in RNA) or deoxyribose (in DNA). The sugar provides the backbone structure of the nucleotide and allows the attachment of the base.

3. Nitrogenous base: This is a heterocyclic ring structure containing nitrogen atoms. There are five major types of nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T), and uracil (U). The specific base attached to the sugar determines the identity of the nucleotide.

These three functional groups are linked together to form a single nucleotide molecule. The phosphate group is attached to the 5' carbon of the sugar, the nitrogenous base is attached to the 1' carbon of the sugar, and the hydroxyl group at the 3' carbon of the sugar is available for bonding to the phosphate group of the next nucleotide in a chain.