What are proteins primarily made of?

Proteins are primarily made of amino acids, which are organic compounds that serve as the building blocks of proteins. Each amino acid contains an amine group, a carboxyl group, and a unique side chain that defines its characteristics. The sequence of amino acids in a protein determines its structure and function, as proteins fold into complex shapes that are essential for their role in biological processes.

Amino acids link together through peptide bonds to form polypeptides, which then fold into functional proteins. This process is crucial in various biological functions, including catalyzing biochemical reactions (as enzymes), providing structural support, facilitating transport, and participating in immune responses.

The other options refer to different macromolecules: fatty acids are the building blocks of lipids; nucleotides are the basic units of nucleic acids like DNA and RNA; and sugars are the monomers that make up carbohydrates. Thus, each option represents a different type of biological macromolecule, making amino acids the correct choice for the main constituents of proteins.