Which macromolecule is composed of chains of amino acids?

Proteins are the macromolecules that are composed of chains of amino acids. The structure of proteins is fundamentally based on the sequence and arrangement of these amino acids, which are connected by peptide bonds. This sequence determines the protein's unique properties and functions in biological systems.

Proteins play critical roles in various cellular processes, including but not limited to enzymatic activity, structural support, transportation of molecules, immune responses, and signaling. Each protein can be thought of as a linear chain that folds into a specific three-dimensional shape, which is crucial for its function.

The other macromolecules listed—carbohydrates, nucleic acids, and fats/lipids—are composed of different types of building blocks. Carbohydrates are formed from sugar molecules, nucleic acids consist of nucleotide units, and fats/lipids are made up of fatty acids and glycerol. Thus, the unique characteristic of proteins being structured from amino acids differentiates them from the other macromolecule categories.