Didesoksynukleotider

Didesoksynukleotider, also known as dideoxynucleotides or ddNTPs, are synthetic analogs of deoxyribonucleotides. They differ from natural deoxyribonucleotides by the absence of a hydroxyl group at the 3' carbon position of the deoxyribose sugar. This seemingly small structural difference has profound implications for DNA synthesis. During DNA replication or PCR, DNA polymerase enzymes add nucleotides to the growing DNA chain by forming a phosphodiester bond between the 3'-hydroxyl group of the last nucleotide and the 5'-phosphate group of the incoming nucleotide. Because dideoxynucleotides lack this crucial 3'-hydroxyl group, they cannot form a phosphodiester bond with the next nucleotide. Consequently, when a dideoxynucleotide is incorporated into a growing DNA strand, DNA synthesis is terminated at that point. This chain-terminating property is the basis for their most significant application: Sanger sequencing, also known as dideoxy sequencing. In this technique, a DNA sample is replicated in the presence of all four natural deoxyribonucleotides (dATP, dCTP, dGTP, dTTP) and a small amount of one type of dideoxynucleotide (ddATP, ddCTP, ddGTP, or ddTTP), each labeled with a different fluorescent dye. This results in a mixture of DNA fragments of varying lengths, each ending with a specific dideoxynucleotide and carrying its corresponding fluorescent label. By separating these fragments by size and detecting their fluorescence, the order of nucleotides in the original DNA sequence can be determined. Dideoxynucleotides also find use in some antiviral therapies, as their incorporation into viral DNA can disrupt viral replication.