DNA's negative charge is on the backbone
- The idea
- Predict
- See it
- Why
- Check
The idea
“DNA is negative because of its bases, the part that carries the code.”
You spend most of your time on A, T, G and C, so they seem like the part that does everything. The charge sits on the outside, on the phosphates.
The short version
The mistake: DNA is negative because of its bases, the part that carries the code.
What's actually true: Every phosphate in the sugar-phosphate backbone carries a negative charge. The bases inside carry none.
- Each nucleotide has a phosphate, a sugar and a base. The phosphates link the sugars into the backbone, and each carries a negative charge.
- The bases carry no charge. They stack in the middle of the helix and pair by hydrogen bonds, which hold the two strands together.
- Both backbones are negative, so they repel each other. Positive ions and histones in the cell offset much of that push.
On the exam: Count phosphates, not bases. Every nucleotide adds one negative charge, whatever its base.