didesoxynucleotides

A dideoxynucleotide, often abbreviated as ddNTP, is a modified nucleotide that is a crucial component in certain molecular biology techniques. Unlike a standard deoxynucleotide, which has a hydroxyl group at the 3' carbon of its sugar ring, a dideoxynucleotide lacks this hydroxyl group. This seemingly small structural difference has profound implications for DNA synthesis.

During DNA replication or in vitro DNA synthesis, new nucleotides are added to the growing DNA strand by forming a phosphodiester bond between the 3' hydroxyl group of the existing strand and the 5' phosphate group of the incoming nucleotide. Because dideoxynucleotides have no 3' hydroxyl group, they cannot form this crucial bond. When a dideoxynucleotide is incorporated into a growing DNA chain, it acts as a chain terminator, preventing further elongation of that particular DNA strand.

This chain-terminating property is the basis for the Sanger sequencing method, also known as the dideoxy method. In Sanger sequencing, a DNA sample is replicated in the presence of all four standard deoxynucleotides (dNTPs) and a small amount of one type of dideoxynucleotide (ddNTP). By using different ddNTPs in separate reactions, or by labeling them with different fluorescent tags, researchers can generate DNA fragments of varying lengths that all end at a specific nucleotide. These fragments are then separated by size, allowing the sequence of the original DNA to be determined. Dideoxynucleotides have been instrumental in the development of DNA sequencing technology and continue to be relevant in molecular biology research.