How does DNA Polymerase add nucleotides?

How does DNA Polymerase add nucleotides?

• A. By Connecting the 3' OH to the 5' Phosphate
• B. By Breaking Hydrogen Bonds
• C. By Connecting the 5' Phosphate Group of the Incoming Nucleotide to the Free 3' Hydroxyl Group of the Previous Nucleotide
• D. By Adding 3' Phosphate to 5' OH

Answer: (C)

DNA polymerase extends the growing DNA strand by forming a phosphodiester bond between the end of the old strand and an incoming nucleotide. The incoming deoxynucleoside triphosphate donates its alpha phosphate (the phosphate at the 5′ end) to the free 3′-hydroxyl group of the last nucleotide in the chain. The 3′-OH acts as a nucleophile, attacking that alpha phosphate, which creates the new backbone linkage and releases pyrophosphate (the two extra phosphates). That is why describing the process as connecting the incoming nucleotide’s 5′ phosphate to the 3′ hydroxyl of the previous nucleotide captures exactly what happens during bond formation. Breaking hydrogen bonds is related to strand separation, not how the nucleotide is added, and adding a 3′ phosphate to a 5′ hydroxyl would not produce the correct phosphodiester linkage.

DNA polymerase extends the growing DNA strand by forming a phosphodiester bond between the end of the old strand and an incoming nucleotide. The incoming deoxynucleoside triphosphate donates its alpha phosphate (the phosphate at the 5′ end) to the free 3′-hydroxyl group of the last nucleotide in the chain. The 3′-OH acts as a nucleophile, attacking that alpha phosphate, which creates the new backbone linkage and releases pyrophosphate (the two extra phosphates). That is why describing the process as connecting the incoming nucleotide’s 5′ phosphate to the 3′ hydroxyl of the previous nucleotide captures exactly what happens during bond formation. Breaking hydrogen bonds is related to strand separation, not how the nucleotide is added, and adding a 3′ phosphate to a 5′ hydroxyl would not produce the correct phosphodiester linkage.