The element found in proteins and nucleic acids but not other organic compounds is nitrogen (N). Nitrogen is the seventh most abundant element in the universe and plays a crucial role in biological molecules. In proteins, nitrogen is present in the amino acid side chains, particularly in amino acids like arginine, lysine, and asparagine. It contributes to the structural integrity and functional properties of proteins by forming peptide bonds and various functional groups. In nucleic acids, nitrogen is a constituent of the nitrogenous bases - adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U). These nitrogenous bases form the building blocks of DNA and RNA molecules, carrying genetic information and enabling essential cellular processes such as protein synthesis. Therefore, nitrogen is an essential element for life and is found exclusively in proteins and nucleic acids, distinguishing them from other organic compounds.