Dideoxy

2,3-Dideoxyribose-a deoxyribose sugars lacking the 3 hydroxyl group;when incorporated into a polynucleotide chain,it blocks further chain elongation.

In DNA, deoxyribonucleic acid, it is the second carbon atom of the ribose molecule that is lacking the hydroxyl group. In RNA the ribose molecule has all five hydroxyl groups.

Dideoxynucleotides are useful in the sequencing of DNA in combination with electrophoresis. A DNA sample which undergoes PCR (polymerase chain reaction) in a mixture containing all four deoxynucleotides and one dideoxynucleotide will produce strands of length equal to the position of each base of the type that complements the type has a dideoxynucleotide present. That is, each nucleotide base of that particular type has a probability of being bonded to not a deoxynucleotide, but rather a dideoxynucleotide, which ends chain elongation. Thus, if the sample is then undergoes electrophoresis, there will be a band present for each length at which the complement of the dideoxynucleotide is present. A sequencing with each of the four dideoxynucleotides separately is the most common method of DNA sequencing.