Each nucleotide consists of a nitrogenous base (T, A, C, or G), the sugar deoxyribose, and a phosphate group.
The 5'
end of the polynucleotide is a phosphate,
while the 3'
end is a hydroxyl group of the sugar.
The phosphate of one nucleotide forms a covalent bond with the sugar of the next, providing a "backbone" from which the bases project.