Question

Looking at the structures of dCTP and ddCMP, what would happen if ddCMP were added to a DNA polymerization reaction?

(A) ddCMP would terminate DNA polymerization because it lacks a 3' OH
(B) ddCMP would terminate DNA polymerization because it is a monophosphate
(C) ddCMP would have no effect on DNA polymerization because it cannot be used as a monmer due to its lack of phosphoanhydride bonds
(D) ddCMP would have no effect on DNA polymerization because it does not resemble dCTP enough to bind to the active polymerization site of DNA polymerase

Answer 1

Adding ddCMP to a DNA polymerization reaction would terminate the process because ddCMP lacks a crucial 3' OH group that is necessary to form the phosphodiester bonds between nucleotides in a growing DNA strand.

Step-by-step explanation:

If ddCMP were added to a DNA polymerization reaction, it would terminate DNA polymerization because it lacks a 3' OH group. This hydroxyl group is necessary for the formation of the phosphodiester bond that links nucleotides together during DNA synthesis. As dCTP is a regular nucleotide triphosphate used by DNA polymerases for synthesizing DNA strands, it has this essential 3' OH group. On the other hand, ddCMP is a dideoxynucleotide which lacks both the 2' and the vital 3' hydroxyl groups. Therefore, when ddCMP is included in a growing DNA strand, it prevents the addition of any further nucleotides, effectively ceasing DNA synthesis.

The dideoxynucleotide does not prevent the addition of further nucleotides due to being a monophosphate or having a structure vastly different from dCTP, nor because of a lack of phosphoanhydride bonds. The crucial factor is the absence of the hydroxyl group at the 3' position of the sugar moiety, which is necessary for the continuation of the DNA polymerization process.