dideoksinukleotidissä

Dideoksinukleotidissä, often abbreviated as ddNTP, refers to a class of nucleotides that lack a hydroxyl group at the 3' carbon position of their deoxyribose sugar. This structural difference, compared to a standard deoxynucleoside triphosphate (dNTP), is crucial for its function in DNA synthesis. In natural DNA synthesis, the 3'-hydroxyl group of a growing nucleotide chain is essential for forming a phosphodiester bond with the incoming dNTP. However, when a ddNTP is incorporated into a DNA strand, the absence of this 3'-hydroxyl group prevents further elongation. This chain-terminating property is the basis for its significant application in molecular biology.

The most well-known use of ddNTPs is in the Sanger sequencing method, also known as the dideoxy chain termination method. In this technique, DNA polymerase is used to synthesize new DNA strands using a template. A mixture of dNTPs and a small amount of a specific ddNTP (ddATP, ddTTP, ddGTP, or ddCTP) is provided. When a ddNTP is randomly incorporated into the growing chain, synthesis stops at that point. By performing this reaction in four separate tubes, each with a different ddNTP, and then separating the resulting fragments by size, the sequence of the original DNA can be determined. Although next-generation sequencing methods have largely superseded Sanger sequencing for large-scale projects, the Sanger method remains valuable for smaller-scale sequencing, verification, and specific applications. Dideoxynucleotides are also used in some antiviral therapies.