Terminator sequence definition8/6/2023 ![]() ![]() ![]() (1) The double-stranded DNA (dsDNA) is denatured into two single-stranded DNA (ssDNA). The Sanger sequencing method consists of 6 steps: Image credit: “Whole-genome sequencing: Figure 1,” by OpenStax College, Biology). According to their sizes, the sequence of the DNA is thus determined.įigure 1. Following synthesis, the reaction products are loaded into four lanes of a single gel depending on the diverse chain-terminating nucleotide and subjected to gel electrophoresis. Compared to dNTPs, ddNTPs has an oxygen atom removed from the ribonucleotide, hence cannot form a link with the next nucleotide. To determine which nucleotide is incorporated into the chain of nucleotides, four dideoxynucleotide triphosphates (ddNTPs: ddATP, ddGTP, ddCTP, and ddTTP) labeled with a distinct fluorescent dye are used to terminate the synthesis reaction. In the presence of the four deoxynucleotide triphosphates (dNTPs: A, G, C, and T), the polymerase extends the primer by adding the complementary dNTP to the template DNA strand. In Sanger sequencing, a DNA primer complementary to the template DNA (the DNA to be sequenced) is used to be a starting point for DNA synthesis. Sanger sequencing remains widely used in the sequencing field as it offers several prominent advantages: (i) cost-efficiency for sequencing single genes and (ii) 99.99% accuracy, especially suitable for verification sequencing for site-directed mutagenesis or cloned inserts. NGS can simultaneously sequence more than 100 genes and whole genomes with low-input DNA. The development of NGS technologies has accelerated genomics research. These fragments were used to assemble larger DNA fragments and, eventually, entire chromosomes. Sanger sequencing was used in the Human Genome Project to determine the sequences of relatively small fragments of human DNA (900 bp or less). Sanger sequencing with 99.99% base accuracy is considered the “gold standard” for validating DNA sequences, including those already sequenced through next-generation sequencing (NGS). This method is designed for determining the sequence of nucleotide bases in a piece of DNA (commonly less than 1,000 bp in length). ![]() Sanger sequencing, also known as the “chain termination method,” was developed by the English biochemist Frederick Sanger and his colleagues in 1977. ![]()
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