In terms of overall electrostatic charge at physiological pH, what is the net charge of DNA and what structural feature is primarily responsible for it?

• A. DNA is negatively charged primarily because the deoxyribose sugars are deprotonated.
• B. DNA is positively charged because its nitrogenous bases carry a net positive charge.
• C. DNA is negatively charged because its phosphate groups in the sugar-phosphate backbone are deprotonated.
• D. DNA is electrically neutral overall because the charges of bases and sugars cancel exactly.

Answer: (C)