Sanger's DNA Squencing

INTRODUCTION

The first DNA sequencing (1968) was performed 15 years after the discovery of the double helix (1953). In 1975, Sanger introduced his “plus and minus” method for DNA sequencing. Sanger’s method, which is also referred to as dideoxy sequencing or chain termination, is based on the use of dideoxynucleotides (ddNTP’s) in addition to the normal nucleotides (NTP’s) found in DNA. Dideoxynucleotides are essentially the same as nucleotides except they contain a hydrogen group on the 3’ carbon instead of a hydroxyl group (OH). These modified nucleotides, when integrated into a sequence, prevent the addition of further nucleotides .This occurs because a phosphodiester bond cannot form between the dideoxynucleotide and the next incoming nucleotide, and thus the DNA chain is terminated. This was a critical transition technique leading to the modern generation of methods that have completely dominated sequencing over the past 30 years.