What Are The Four Nucleotides

Figure 2: The four ddNTPs.

As described above, the adjacent major step in the Sanger process is to expose the target sequence to DNA polymerase and significant amounts of all four nucleotides. In their unbound form, nucleotides accept iii phosphate groups and are formally called deoxynucleotide triphosphates, or dNTPs (where the "N" is a placeholder for A, T, G, or C). During the construction of a new Deoxyribonucleic acid strand, a molecule chosen a hydroxyl group (which contains an oxygen atom and a hydrogen atom) attaches to the sugar of the final dNTP in the strand and chemically binds to the phosphate group on the next dNTP. This binding causes the Dna chain to grow. In Sanger sequencing, nevertheless, a special blazon of "dummy" nucleotide is included with the regular dNTPs that surround the growing DNA strand. These special nucleotides are known every bit dideoxynucleotide triphosphates, or ddNTPs (Figure 2), and they lack the crucial hydroxyl group that is attached to the sugar of dNTPs. Therefore, whenever a ddNTP is added to a growing Deoxyribonucleic acid strand, it is unable to chemically demark with the next nucleotide in the chain, and the DNA strand stops growing.

When researchers carry out the Sanger procedure, they are manipulating many copies of the template strand at in one case, and then an glut of dNTPs is required in order for Deoxyribonucleic acid synthesis to proceed unimpeded on these copies until a ddNTP is added. Then, after the supply of dNTPs has been exhausted, the final result of the sequencing experiment is a group of new DNA strands of varying lengths. These strands all have a terminal ddNTP that indicates whether an A, T, G, or C occurs in that position on the template strand (Figure three).