Proteins are primarily composed of which of the following elements?

Proteins are macromolecules essential for numerous biological functions and their structure is primarily composed of carbon, hydrogen, oxygen, and nitrogen. Each protein is built from a set of 20 different amino acids, which are organic compounds that contain these elements in varying proportions.

Carbon serves as the backbone for the amino acids, while hydrogen and oxygen are integral parts of the functional groups attached to these carbon atoms. Nitrogen is a key component found in the amino group of each amino acid, which differentiates them from carbohydrates and lipids.

The other choices include elements not typically found in protein structures. Sulfur, while present in some amino acids (like cysteine and methionine), is not a primary component of proteins in general. Phosphorus is mainly associated with nucleic acids and energy transfer molecules like ATP, not proteins. Helium is a noble gas that does not play any role in biological molecules. Understanding the elemental composition of proteins is crucial for grasping their biological roles and the nature of their interactions within the body.