Question

If a nucleoside monophosphate is used instead of nucleotide triphosphate in polymerisation reaction during DNA replication, select the most appropriate consequence:

• A. The nucleoside monophosphate is not incorporated into the existing DNA strand
• B. The nucleoside monophosphate is incorporated into the existing DNA strand
• C. The nucleoside is incorporated into the existing DNA strand after the removal of phosphate group
• D. The nucleoside monophosphate gets an additional phosphate and nucleoside bisphosphate gets added to the existing DNA

Answer 1

The correct option is A The nucleoside monophosphate is not incorporated into the existing DNA strand

During the synthesis of complementary daughter strands, DNA polymerase uses deoxyribonucleotide triphosphates (dNTPs) as substrates. dNTPs as substrates perform dual role:-
- They get added to the 3’ OH after losing a molecule of pyrophosphate and help in strand elongation.
- The two terminal phosphate molecules which get released in the form of PPi provide energy during the process of polymerization.
If dNMPs or deoxyribonucleoside monophosphates are utilized during polymerisation reactions, it can’t be utilized as a substrate by DNA polymerase III. This is because each and every enzyme has a specific substrate which fits into its active site. Since dNMPs and dNTPs differ in their size and molecular structures, dNMPs won’t get recognized as a substrate by DNA polymerase enzymes. Additionally, dNMPs won’t liberate pyrophosphate, hence, won’t yield energy needed for the polymerization to occur.