In the DNA double helix, what structural feature gives DNA an overall negative charge at physiological pH?

• A. The hydrogen bonds between complementary bases
• B. The deoxyribose sugars in the backbone
• C. The hydrophobic stacking interactions among the nitrogenous bases
• D. The phosphate groups in the sugar-phosphate backbone

Answer: (D)

Verified step by step guidance

1. Recall the structure of the DNA double helix, which consists of a sugar-phosphate backbone and nitrogenous bases paired in the interior.
2. Identify the components of the backbone: deoxyribose sugars and phosphate groups. Understand that the phosphate groups carry a charge.
3. Consider the chemical nature of phosphate groups: at physiological pH, phosphate groups lose protons and carry negative charges.
4. Recognize that hydrogen bonds between bases and hydrophobic stacking interactions do not contribute to the overall charge of DNA.
5. Conclude that the negative charge of DNA at physiological pH is due to the phosphate groups in the sugar-phosphate backbone.