Sanger Sequencing — Quiz

Sample Answer: ddNTPs (dideoxynucleotides) are modified nucleotides that lack a 3′-OH group on the deoxyribose sugar. When incorporated during DNA synthesis by DNA polymerase, they terminate the growing DNA strand because no further nucleotides can be added. In Sanger sequencing, a mixture of dNTPs and a small proportion of fluorescently-labeled ddNTPs is used. As DNA polymerase extends the primer, random incorporation of ddNTPs produces fragments of different lengths, each terminating at a different position. These fragments are separated by capillary electrophoresis and the fluorescent labels are read by a laser to determine the DNA sequence.