Why do ddNTP’s cause chain termination during Sanger’s DNA sequencing method? Write the DNA fragments formed by chain termination for the given original DNA strand-3’ ATGCTAGC 5’.
Answers
Sanger sequencing involves making many copies of a target DNA region. Its ingredients are similar to those needed for DNA replication in an organism, or for polymerase chain reaction (PCR), which copies DNA in vitro. They include:
A DNA polymerase enzyme
A primer, which is a short piece of single-stranded DNA that binds to the template DNA and acts as a "starter" for the polymerase
The four DNA nucleotides (dATP, dTTP, dCTP, dGTP)
The template DNA to be sequenced
However, a Sanger sequencing reaction also contains a unique ingredient:
Dideoxy, or chain-terminating, versions of all four nucleotides (ddATP, ddTTP, ddCTP, ddGTP), each labeled with a different color of dye
cleotides can be added. The chain ends with the dideoxy nucleotide, which is marked with a particular color of dye depending on the base (A, T, C or G) that it carries.