What are proteins primarily made of?

Proteins are primarily made of amino acids arranged in a linear chain. This linear arrangement of amino acids is known as a polypeptide chain, which then folds into specific three-dimensional structures that determine the protein's function. Each protein's unique sequence of amino acids, determined by the genetic code, dictates how it will fold and what role it will play in the body, such as catalyzing biochemical reactions, providing structural support, or facilitating communication between cells.

The other options describe components of different biomolecules. Amino acids themselves are the building blocks of proteins, but they do not form circular structures; rather, they link together in a sequence. Carbohydrates, composed of sugar units, are distinct from proteins. Lastly, nucleotides are the building blocks of nucleic acids like DNA and RNA, not proteins. Thus, understanding that proteins consist of linear chains of amino acids is essential for grasping fundamental aspects of biochemistry and nutrition.