During a DNA sequencing experiment, the researcher adds all the required components to the reaction, but accidentally adds only one of the four dideoxynucleotides, the ddC. What products will be observed after this reaction is complete?
A) All fragments will end in A.
B) All fragments will end in C.
C) All fragments will end in G.
D) All fragments will end in T.
E) No fragments will be made.

Question

Quizplus · Accepted Answer

When ddC (dideoxycytidine) is added to a DNA sequencing reaction, it gets incorporated into the growing DNA strand in place of the normal nucleotide (dC). Since ddC lacks the 3' hydroxyl group necessary for forming a phosphodiester bond with the next nucleotide, the DNA chain elongation stops whenever ddC is incorporated. Therefore, all DNA fragments produced in this reaction will end in C, as ddC terminates the extension of the DNA strand at every point where a cytosine (C) would normally be incorporated.

During a DNA Sequencing Experiment, the Researcher Adds All the Required