The negative charge of the DNA molecule comes from the phosphate groups in its backbone. Each nucleotide in DNA consists of a sugar (deoxyribose), a nitrogenous base, and a phosphate group. The phosphate groups link the sugars of adjacent nucleotides via phosphodiester bonds, forming the sugar-phosphate backbone of DNA. Specifically, the phosphate group in each nucleotide carries a negative charge because one of its oxygen atoms remains ionized (loses a proton) at physiological pH, leaving behind a negatively charged oxygen. This negative charge is retained even when the phosphate forms phosphodiester bonds linking nucleotides, as one negative charge remains on each phosphate group. This gives the entire DNA molecule an overall negative charge
. In summary:
- The phosphate group in each nucleotide is responsible for the negative charge on DNA.
- The negative charge arises from the ionization of oxygen atoms in the phosphate group.
- This negative charge is consistent along the sugar-phosphate backbone of DNA, making the molecule negatively charged overall.
This negative charge is biologically important because it influences DNA's interactions with proteins (such as histones) and its behavior in techniques like gel electrophoresis
