In the Sanger dideoxy method for DNA sequencing a small amou

In the Sanger (dideoxy) method for DNA sequencing, a small amount of a dideoxynucleoside triphosphate-say, ddCTP-is added to the sequencing reaction along with a larger amount of the corresponding dCTP. What result would be observed if the dCTP were omitted? What purpose would adjusting the ratio of dNTP to ddNTP serve in Sanger sequencing?

Solution

In Sanger\'s method ddNTPs are added along with dNTPs. ddNTPs are di-deoxy-nucleotide-tri-phosphates. They lack oxygen at 2^nd and 3^rd position of ribose sugar. As a result, the 3^rd sugar position does not have “O” to form phosphodiester bond with the next nucleotide. So, if you add ddCTP, DNA synthesis will stop after every ‘C’ present in the parent strand.