What happens to the phosphates during nucleotide addition?

What happens to the phosphates during nucleotide addition?

• A. Three Phosphates Are Released
• B. It Is Released During the Hydration Reaction
• C. Two Phosphates Are Released During the Dehydration Reaction
• D. No Phosphates Are Released

Answer: (C)

In nucleotide addition during DNA synthesis, the incoming nucleotide is a triphosphate. The growing strand’s 3′-OH attacks the alpha phosphate of this nucleotide, forming a phosphodiester bond and releasing the beta and gamma phosphates as pyrophosphate. This is a dehydration (condensation) step, and the two phosphates are released rather than all three. Often, pyrophosphate is quickly hydrolyzed to two inorganic phosphates, which helps drive the reaction forward. So, two phosphates are released during the dehydration step, making that option the correct description.

In nucleotide addition during DNA synthesis, the incoming nucleotide is a triphosphate. The growing strand’s 3′-OH attacks the alpha phosphate of this nucleotide, forming a phosphodiester bond and releasing the beta and gamma phosphates as pyrophosphate. This is a dehydration (condensation) step, and the two phosphates are released rather than all three. Often, pyrophosphate is quickly hydrolyzed to two inorganic phosphates, which helps drive the reaction forward. So, two phosphates are released during the dehydration step, making that option the correct description.