• a five-carbon deoxyribose sugar
• a phosphate group
• a nitrogen-containing base

Two chains of nucleotides twist around each other to form a double helix with sugar-phosphate backbones held together by hydrogen bonds between the nitrogen-containing bases.

The hydrogen bonding between the nitrogen-containing bases occurs in complementary base pairs:

• Adenine (A) always pairs with Thymine (T).
• Guanine (G) always pairs with Cytosine (C).