What is the overall charge of DNA?

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

Answer: (B)

DNA has an overall negative charge because its backbone is made of sugar and phosphate groups, and the phosphate groups are negatively charged at the pH inside living cells. Each phosphate adds a negative charge, so the many phosphates along the long DNA molecule produce a net negative charge. The bases themselves are mostly uncharged, so they don’t offset those phosphate charges. This negative charge is a key reason DNA interacts with positively charged proteins and ions in the cell, and why ions like Na+ and Mg2+ help shield and stabilize DNA in solution. The term polar describes how charge is distributed within a molecule, which DNA certainly has, but the question is about the overall net charge, which is negative.