In DNA structure, what overall net charge does DNA carry at physiological pH, and what feature of the molecule is primarily responsible for this charge?

• A. Net positive charge, primarily due to protonated nitrogenous bases
• B. Net negative charge, primarily due to the phosphate groups in the sugar-phosphate backbone
• C. Net neutral charge, primarily because deoxyribose sugars are uncharged and dominate the molecule
• D. No net charge, because positive charges on bases exactly cancel negative charges on phosphates

Answer: (B)