The answer is all of the above.
Both nitrogen and carbon are present in DNA, proteins and, as well, amino acids.
Amino acids are compounds that contain a carboxyl group (carbon containing) and an amino group (nitrogen containing). Amino acids are building blocks of protein, thus, nitrogen and carbon are needed in both proteins and amino acids.
DNA building blocks are nucleotides. Nucleotides contain a nitrogenous base, a five-carbon sugar, and, at least, one phosphate group.
