DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are called acids because of their chemical structure, which includes phosphate groups that release hydrogen ions (H+) in solution, making them acidic. The name ‘nucleic acid’ reflects this acidic property.
Both DNA and RNA are composed of nucleotides, which contain a sugar molecule, a nitrogenous base, and a phosphate group. The phosphate group is the component that contributes to the acidic characteristic. When these nucleotides link together to form a chain, the phosphate backbone forms repeats of phosphate-sugar units.
When DNA and RNA are in solution, the phosphate groups can release protons, increasing the acidity of the solution. This is similar to how other acids behave in a solution. Therefore, the naming of these essential biological molecules as acids is primarily a reflection of their chemical properties rather than their biological function.