Which of the following elements are present in all proteins? 1. I. Carbon 2. II. Hydrogen 3. III. Oxygen 4. IV. Nitrogen Select the correct answer from the codes given below:

1. The question asks which elements are present in all proteins. 2. Proteins are macromolecules made up of long chains of amino acids linked by peptide bonds. 3. Every amino acid has a fundamental structure consisting of a central carbon atom bonded to: an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom (-H), and a variable side chain (R group). 4. From this basic structure, we can see that: - The central atom and carboxyl group contain Carbon (C). - The structure includes Hydrogen (H) atoms. - The carboxyl group contains Oxygen (O). - The amino group contains Nitrogen (N). 5. Since all proteins are composed of amino acids, all proteins must contain these four essential elements: Carbon (I), Hydrogen (II), Oxygen (III), and Nitrogen (IV).