didesoksynukleotidi

A dideoxynucleotide, often abbreviated as ddN, is a modified nucleotide that lacks a hydroxyl group at the 3' position of the deoxyribose sugar. This structural difference is crucial because in normal DNA synthesis, the 3' hydroxyl group is essential for forming the phosphodiester bond that links one nucleotide to the next. When a dideoxynucleotide is incorporated into a growing DNA chain by a DNA polymerase, the absence of this 3' hydroxyl group prevents further elongation. Consequently, the DNA synthesis terminates at that point.

Dideoxynucleotides are most famously known for their application in the Sanger sequencing method, also known as dideoxy sequencing. In this technique, DNA is replicated in the presence of all four normal deoxynucleotides (dATP, dGTP, dCTP, and dTTP) along with a small amount of one of the four dideoxynucleotides (ddATP, ddGTP, ddCTP, or ddTTP). Each type of dideoxynucleotide is labeled with a different fluorescent marker. When a dideoxynucleotide is incorporated into a DNA strand, replication stops. By performing four separate reactions, each with a different dideoxynucleotide, or by using differentially labeled dideoxynucleotides in a single reaction, a collection of DNA fragments of varying lengths is generated, each ending with a specific dideoxynucleotide. These fragments can then be separated by size, and the order of the dideoxynucleotides (and thus the original DNA sequence) can be determined by the color of the fluorescent label at the end of each fragment.