This method helps in sequencing the linear as well as the circular DNA. The first step involves heat treatment for denaturing the DNA into the single-stranded structure. Next step involves annealing the primer to one of the strands. The primer used in the DNA synthesis consists of an oligonucleotide. The DNA synthesized through this step ensures complementarity with the sequence of interest. Each sequencing experiment requires four set of reactions. The components include single-stranded DNA (to be sequenced), oligonucleotide primer, DNA polymerase, nucleotide precursors such as dATP, dCTP, dGTP, dTTP, and a small amount of dideoxynucleotide ddNTP. A dideoxynucleotide is a modified version of deoxynucleotide. Its deoxyribose sugar consists of a 3’-H instead of 3’-OH. Labeling the primers or the precursors helps in determining the newly synthesized DNA. The reactions consisting of the modified deoxynucleotides or the dideoxynucleotides differ from the others. These modified precursors get added in the reaction mixture to about one-hundredth the amount of unmodified precursor. Upon extension of the primer, the DNA polymerase occasionally adds a dideoxynucleotide. After this step, the DNA synthesis stops. Since the dideoxynucleotide does not have a 3’-OH, a new phosphodiester bond cannot form. Hence, every DNA synthesized using this method consists of a dideoxynucleotide at its end.