What are proteins made of?

Proteins are fundamentally composed of amino acids, which are organic compounds that serve as the building blocks of proteins. In the process of protein synthesis, amino acids link together through peptide bonds to form long chains. There are 20 different amino acids that can combine in various sequences to create a vast array of proteins, each with unique structures and functions. The specific sequence and arrangement of these amino acids ultimately determine the protein's shape and function, making them essential for various biological processes, including enzyme activity, structure, and transport among others.

While the other options represent important biological macromolecules, they do not relate directly to the composition of proteins. Nucleotides are the building blocks of nucleic acids like DNA and RNA, fatty acids are components of lipids, and carbohydrates consist of sugars and starches, which serve different roles in biological systems. Thus, the correct identification of amino acids as the primary constituents of proteins is crucial to understanding their structure and function in living organisms.