DNA's charge?

DNA's charge?

• A. Positive
• B. Negative
• C. Neutral
• D. Undefined

Answer: (B)

DNA carries a negative charge because of its sugar–phosphate backbone. Each phosphate group is acidic and loses protons in solution, leaving a negative charge. With many nucleotides lined up in the molecule, these negative charges accumulate, making DNA a polyanion under physiological conditions. This negative charge is why DNA migrates toward the positive electrode in gel electrophoresis and why it interacts with positively charged proteins like histones to form chromatin. In short, the phosphate groups ensure DNA is negatively charged, not positive or neutral.

DNA carries a negative charge because of its sugar–phosphate backbone. Each phosphate group is acidic and loses protons in solution, leaving a negative charge. With many nucleotides lined up in the molecule, these negative charges accumulate, making DNA a polyanion under physiological conditions. This negative charge is why DNA migrates toward the positive electrode in gel electrophoresis and why it interacts with positively charged proteins like histones to form chromatin. In short, the phosphate groups ensure DNA is negatively charged, not positive or neutral.