Sequencing methods

DNA, or deoxyribonucleic acid, forms a double-stranded helix. Each strand consists of a sequence of nucleotides, themselves made up of three components: a five-carbon sugar (deoxyribose for DNA and ribose for RNA), a phosphate group and a nitrogenous base: adenine, cytosine, guanine or thymine, often represented by the initials A, C, G and T for DNA, and A, C, G and U (uridine) for RNA. Nucleotide chains are formed by a phosphodiester bond between the OH of the first nucleotide (at C3′ of the deoxyribose) and the phosphate at C5′ of the second nucleotide. Thus, the second nucleotide has an OH available at C3′ to bind to the phosphate of a third nucleotide and so on (figure 1 a ). Synthesis as well as orientation of...