nucleic acid

This term refers specifically to the biopolymers DNA and RNA. In scientific discourse, it is treated as a mass noun when referring to the chemical substance in general, though it can be used countably when discussing different types or specific molecules of nucleic acids.

Because it is a technical term from biochemistry, it is almost exclusively used in formal, academic, or medical registers. It is rarely used in casual conversation unless the speaker is discussing genetics or molecular biology.