Protein molecules always contain Carbon, Oxygen, Hydrogen and Nitrogen. Occasionally, they will contain Sulphur - such as Cysteine, Methionine, and Cystine. A Phosphate (Phosphurus) is also used in other derivations and biosyntheses: Glutamate-5-Phosphate is produced when Proline is synthesized from Glutamate. A Carbamoyl-Phosphate is used in the Urea Cycle: a process which converts toxic Ammonia into urea or uric acid so the organism can more easily process and utilize Nitrogen (N) without the build up of Ammonia (NH3) during protein digestion.
4 atoms protein molecules always contain are nitrogen, oxygen, hydrogen and carbon. They sometimes also contain disulfide bonds ( sulfur ), and calcium