Proteins that are made of repeating units of amino acids are called what?

The correct answer refers to the structure of proteins, which are indeed made up of long chains of amino acids linked together by peptide bonds. When we talk about "repeating units of amino acids," we are specifically discussing polypeptides, which are the chains formed when amino acids are joined together in this manner.

Proteins can be thought of as a higher-level organization of polypeptides; they may consist of one or more polypeptide chains that are folded into a specific three-dimensional shape, which is crucial for their biological function. Each protein's unique sequence of amino acids ultimately dictates its structure and function.

While enzymes are a specific type of protein that catalyze biochemical reactions, carbohydrates are a distinct class of biomolecules completely unrelated to amino acids. Therefore, the term "protein" does encompass polypeptides, but it refers more broadly to the final functional molecules formed from these chains. Understanding the relationship between polypeptides and proteins helps to clarify why the answer is framed in the context of proteins composed of amino acids.