What are the building blocks of proteins?

Proteins are composed of smaller units known as amino acids, which serve as their building blocks. Each amino acid has a specific structure that includes an amino group, a carboxylic acid group, and a variable side chain known as an R group. The sequence and arrangement of these amino acids determine the structure and function of the resulting protein. When amino acids link together through peptide bonds, they form polypeptides, which can fold into complex three-dimensional shapes — an essential feature for their role in biological functions ranging from catalyzing metabolic reactions as enzymes to providing structural support in cells.

In contrast, sugars are carbohydrates that serve primarily as energy sources or structural components, nucleotides are the building blocks of nucleic acids like DNA and RNA, and fatty acids are components of lipids, which make up cell membranes and serve various other roles in biology. Thus, the distinct role of amino acids as the fundamental units of protein synthesis underlines why they are recognized as the building blocks of proteins.