Here's why:

* Nucleic Acids: DNA and RNA are made up of nucleotides, which consist of a sugar molecule (deoxyribose or ribose), a phosphate group, and a nitrogenous base. All of these components contain carbon atoms.

* Proteins: Proteins are made up of amino acids, which are composed of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a side chain (R-group). The R-group varies between different amino acids, but all of them have carbon as a key component.

In short, carbon is the fundamental building block for both nucleic acids and proteins, making it a crucial element in the structure and function of these essential biomolecules.