dideoksynukleotidet

Dideoksynukleotidet, often abbreviated as ddNTPs, are a class of nucleotide analogs that play a crucial role in molecular biology, particularly in DNA sequencing. Unlike natural deoxynucleotides (dNTPs), dideoxynucleotides lack a hydroxyl group at the 3' position of their deoxyribose sugar. This seemingly small structural difference has significant implications for DNA synthesis.

During DNA replication or enzymatic DNA synthesis, 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 the 3'-hydroxyl group, they cannot form this phosphodiester bond when incorporated into a DNA strand. As a result, the addition of a dideoxynucleotide effectively terminates the elongation of the DNA chain.

This chain-terminating property is the foundation of the Sanger sequencing method, also known as the dideoxy chain-termination method. In Sanger sequencing, a mixture of dNTPs and a small amount of a specific ddNTP (labeled with a fluorescent dye or radioisotope) is used in a DNA synthesis reaction. This results in a collection of DNA fragments of varying lengths, each ending with the specific ddNTP. By separating these fragments by size and detecting the label, the sequence of the original DNA can be determined. Dideoksynukleotidet are therefore essential tools for understanding genetic information.