The new nucleotide brings its own energy
- The idea
- Predict
- See it
- Why
- Check
The idea
“Every building step needs its own ATP, so DNA polymerase spends one per nucleotide.”
You've seen ATP pay for pumps and muscles, so it seems every new bond needs one. DNA's building blocks arrive carrying their own energy.
The short version
The mistake: Every building step needs its own ATP, so DNA polymerase spends one per nucleotide.
What's actually true: Each nucleotide arrives with three phosphates. Releasing two of them pays for its bond, so no separate ATP is spent.
- DNA is built from dNTPs, nucleotides with three phosphates. Like ATP, they release energy when phosphates break off.
- As a dNTP joins the 3' end, one phosphate stays in the backbone. The other two leave, and that powers the bond.
- The cell paid earlier, using ATP to make the dNTPs. Other replication jobs use ATP too, like helicase unwinding the helix.
On the exam: Triphosphate building blocks pay for their own bond. Look for two phosphates leaving, not a separate ATP.