The three components that make up a nucleotide are a sugar molecule, a phosphate molecule and one of the four nitrogenous bases. These three components form the double helix shape of DNA.
A nucleotide is a basic structural unit of nucleic acids, such as DNA and RNA. The sugar molecule is either ribose or deoxyribose, and the bases are adenine, cytosine, guanine and thymine. These three components fit together in a double helix shape.
Adenine and guanine are purine bases that have a double ring structure. Cytosine and thymine are pyrimidine bases that have a single ring structure. A purine base always pairs with a pyrimidine base. It follows that a thymine molecule only pairs with an adenine molecule and a guanine molecule only pairs with a cytosine molecule.
The structure of the nitrogenous bases for a nucleotide helped biologist James Watson and physicist Francis Crick determine the double helix structure, or twisted ladder shape, of DNA in 1953. The sugar and phosphate components form the two long strands of the ladder. The base pairs, adenine and thymine or cytosine and guanine, constitute the rungs of the ladder.