Chain termination
Chain Termination
Chain termination is a critical concept in the field of molecular biology, particularly in the context of DNA replication and DNA sequencing. It refers to the process by which the elongation of a DNA strand is halted, preventing further addition of nucleotides. This mechanism is essential for various laboratory techniques, including the widely used Sanger sequencing method.
Mechanism of Chain Termination[edit | edit source]
In the context of DNA replication, chain termination occurs when a nucleotide analog, known as a dideoxynucleotide (ddNTP), is incorporated into the growing DNA strand. Unlike normal deoxynucleotides (dNTPs), ddNTPs lack a 3' hydroxyl group on the sugar moiety. This absence prevents the formation of a phosphodiester bond with the next nucleotide, effectively terminating the chain.
Dideoxynucleotides[edit | edit source]
Dideoxynucleotides are chemically modified nucleotides that play a crucial role in chain termination. They are similar to regular nucleotides but are missing the 3' hydroxyl group. When a ddNTP is incorporated into a DNA strand during replication or sequencing, it stops further elongation because the necessary 3' hydroxyl group required for the addition of the next nucleotide is absent.
Application in Sanger Sequencing[edit | edit source]
Sanger sequencing, also known as the chain termination method, utilizes ddNTPs to determine the sequence of DNA. During the sequencing process, a mixture of normal dNTPs and labeled ddNTPs is used. When a ddNTP is incorporated, it results in the termination of the DNA strand. By running the resulting fragments on a gel or through a capillary electrophoresis system, the sequence of the DNA can be deduced based on the length of the terminated fragments.
Importance in Molecular Biology[edit | edit source]
Chain termination is not only fundamental to DNA sequencing but also to understanding the mechanisms of DNA replication and polymerase chain reaction (PCR). It provides insights into how DNA polymerases function and how they can be manipulated for various biotechnological applications.
Also see[edit | edit source]
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