Each phosphate group in the DNA backbone carries what charge?

Each phosphate group in the DNA backbone carries approximately one negative charge at physiological pH.

DNA’s phosphate groups are part of phosphodiester linkages joining neighboring deoxyribose sugars. Under normal cellular conditions, these acidic groups are ionized, leaving the backbone negatively charged. Because the charge is repeated along both strands, DNA is a strongly anionic molecule overall.

That negative charge affects how DNA behaves. It attracts positively charged histone proteins, which help compact DNA inside the nucleus, as well as positively charged ions such as magnesium. The charge also causes electrostatic repulsion between nearby DNA segments, so cells need proteins and ions to help fold and package the molecule efficiently.

The answer is often simplified to “negative one” for quiz purposes. In detailed chemical descriptions, the exact protonation state can depend on pH and the surrounding environment, and counterions partially neutralize DNA in cells. That does not change the standard biological fact: each backbone phosphodiester contributes roughly one negative elementary charge at physiological pH. The bases themselves are not responsible for DNA’s characteristic overall negative charge.