Probably the most structuraly complex molecules known. Polypeptide backbone has many different amino acid side chains attached to it. Many of the covalent bonds allow free rotation, the chain can fold in an enormous number of ways. There are a huge number of 3D shapes a protein can be in due to the folding of the polypeptide chain. The nitrogen containing rings are referred to as bases.
Most fundamental role is the storage and retrieval of biological information.
Genetic information directs the synthesis of proteins. DNA does not direct protein synthesis itself, RNA is used as an intermediate. Nucleotides can also serve as short-term carriers of energy. ATP participates in the transfer of energy.