Chemical composition of a protein molecule.

• A. C H O
• B. C H O N S
• C. C H O N
• D. C H O N P

Answer: (C)

Proteins are built from amino acids, and each amino acid contains carbon, hydrogen, oxygen, and nitrogen. Those four elements make up the core of nearly all protein molecules. Sulfur does appear in some amino acids (like cysteine and methionine), so some proteins have sulfur, but it isn’t a universal component. Phosphorus isn’t a typical part of the protein backbone. So the most accurate general composition is carbon, hydrogen, oxygen, and nitrogen.