Dideoxyribonucleotide

Dideoxyribonucleotide is a modified nucleotide used in the Sanger Method of DNA sequencing. Its structure is that of a ribonucleotide, with OH groups replaced with H groups at the 2' and 3' positions of the ribose ring.

The role it plays in DNA sequencing is based on the fact that deoxyribonucleoside triphosphates (which are the building blocks of DNA) allow DNA chain synthesis to occur through a condensation reaction between the 5' phosphate (following the cleavage of pyrophospate) of the current nucleotide with the 3' hydroxyl group of the previous nucleotide. The dideoxyribonucleosides do not possess a 3' hydroxyl group, hence no further chain elongation can occur once this dideoxynucleotide is on the chain. This can lead to the determination of the DNA sequence.