terminaattorinuukleotidi

Terminaattorinuukleotidi, also known as a chain-terminating nucleotide or dideoxynucleotide, is a modified nucleotide that plays a crucial role in molecular biology, particularly in DNA sequencing and some antiviral therapies. Unlike standard deoxynucleotides, which have a hydroxyl group at the 3' carbon position of their sugar ring, terminaattorinuukleotidi lacks this hydroxyl group.

This structural difference is the key to its function. During DNA synthesis, DNA polymerase adds new nucleotides by forming a phosphodiester bond between the 3' hydroxyl group of the growing DNA strand and the 5' phosphate group of the incoming nucleotide. Because terminaattorinuukleotidi lacks the 3' hydroxyl group, it cannot form this phosphodiester bond. Therefore, when a terminaattorinuukleotidi is incorporated into a growing DNA chain, it effectively terminates further elongation.

This property is exploited in the Sanger sequencing method. In this technique, DNA is replicated in the presence of a mixture of normal deoxynucleotides and a small amount of modified terminaattorinuukleotidi. Each type of terminaattorinuukleotidi (dATP, dCTP, dGTP, dTTP) is labeled with a different fluorescent dye. When a terminaattorinuukleotidi is incorporated, the DNA synthesis stops at that specific point. By running the resulting terminated DNA fragments on a gel or using capillary electrophoresis, the order of the incorporated terminaattorinuukleotidi can be determined, revealing the original DNA sequence. Terminaattorinuukleotidi are also the basis for several antiviral drugs, such as zidovudine (AZT), which inhibit viral DNA replication by terminating the synthesis of viral genetic material.