Each nucleotide consists of three components:
a nitrogenous base: cytosine (C), guanine (G), adenine (A) or thymine (T)
a five-carbon sugar molecule (deoxyribose in the case of DNA)
a phosphate molecule
The backbone of the polynucleotide is a chain of sugar and phosphate molecules. Each of the sugar groups in this sugar-phosphate backbone is linked to one of the four nitrogenous bases.