What are proteins primarily composed of?

Proteins are primarily composed of chains of amino acids, which are the building blocks of proteins. Each amino acid consists of an amino group, a carboxyl group, a hydrogen atom, and a distinctive side chain or R group that determines the properties of the amino acid. The sequence of amino acids in a protein is critical because it dictates the protein's structure and function.

When amino acids link together through peptide bonds, they form polypeptides, which can fold into complex three-dimensional structures. This folding is essential for the protein to perform its specific biological functions, such as acting as enzymes, transporting molecules, or providing structural support within cells.

In contrast, the other choices refer to different types of biological macromolecules. Fatty acids that are linked together contribute to lipids, while monosaccharides connected via glycosidic bonds form carbohydrates, and nucleotides in long strands make up nucleic acids like DNA and RNA. Each group plays distinct roles in biological systems, highlighting the unique composition and function of proteins within the cell.