The molecules that make up the backbone of DNA are deoxyribose and a phosphate group, according to the Physiology Department of the University of Illionis at Chicago. Deoxyribose is a five-carbon sugar. The phosphate group contains one phosphorus atom bonded to four oxygen atoms.
The phosphate group links to a certain carbon atom on deoxyribose, which is called the 5' carbon. Another carbon on this sugar molecule, called the 3' carbon, links to another phosphate group. The Physiology Department of the University of Illinois at Chicago refers to this connection as a 3'-5' phosphodiester linkage. The Scitable website states that the deoxyribose bonds with one of the four nucleotide bases (adenine, guanine, thymine and cytosine) to form a nucleotide, a subunit of the DNA molecule.