The essential components of a nucleotide are a pentose (five carbon sugar), a nitrogenous base and one to three phosphate groups. The combinations of possible pentoses, bases and phosphate groups create several different nucleotides.
In nature, two different sugar backbones are present in nucleic acids. Deoxyribose is present in DNA, and ribose is present in RNA. The only difference between these two sugars is that deoxyribose has two hydrogens bound to its 2' carbon instead of a hydrogen and a hydroxyl group as in ribose. The different nitrogenous bases are what are referred to by the letters typically thought of as the genetic code. These stand for adenine, thymine, uracil, guanine and cytosine. These molecules are all one- or two-ring structures that contain nitrogen atoms. Finally, the number of phosphate groups attached to the base determines how much energy is stored in the molecule.