Question

In the Sanger method of DNA sequencing, what causes the termination of chain elongation?

a) Denaturation of the double-stranded DNA fragments.
b) When denaturation causes the primers to disassociate from the strands.
c) The incorporation of a dideoxynucleotide.
d) The incorporation of a regular DNA nucleotide.
e) When the DNA polymerase encounters a stop codon.

Answer 1

The termination of chain elongation in the Sanger method of DNA sequencing is caused by the incorporation of a dideoxy nucleotide (ddNTP), which lacks the necessary 3' OH group for further elongation. This results in DNA fragments of various lengths that can be sequenced.

Step-by-step explanation:

In the Sanger method of DNA sequencing, what causes the termination of chain elongation is c) The incorporation of a dideoxy nucleotide (ddNTP).

The Sanger method, also known as the chain termination method or the dideoxy method, involves using a single-stranded DNA as a template. DNA polymerase synthesizes the complementary strand by adding nucleotides that are complementary to the template. Regular deoxynucleotides (dNTPs) are added to this growing strand; however, when a dideoxy nucleotide is incorporated, it lacks the essential 3' OH group that is necessary for the addition of the next nucleotide. Therefore, the DNA chain elongation is terminated at this point, resulting in DNA fragments of various lengths. These fragments can then be analyzed via electrophoresis in order to deduce the DNA sequence.

By using dideoxy nucleotides labeled with different fluorescent dyes, each terminated fragment can be identified, allowing for the sequence of nucleotides in the DNA to be determined by the color code on an electropherogram after capillary electrophoresis.