What is the basic building block of proteins?

The basic building block of proteins is the amino acid. Amino acids are organic compounds that contain a central carbon atom, an amino group, a carboxyl group, and a distinctive side chain or R group that determines the unique properties of each amino acid. Proteins are polymers formed by linking together these amino acids through peptide bonds, creating long chains that fold into specific three-dimensional structures essential for their function.

Each protein's specific sequence of amino acids will dictate its unique shape and ultimately its function within biological systems. This is critical because the structure of a protein influences how it interacts with other molecules, which is fundamental to the myriad roles proteins play in the body, including catalyzing metabolic reactions, supporting cellular structure, transporting molecules, and acting as signaling molecules.

The other options represent different types of biological macromolecules: nucleotides are the building blocks of nucleic acids like DNA and RNA, fatty acids are components of lipids which contribute to cell membranes and energy storage, and carbohydrates serve as energy sources and structural components but are not related to protein structure. Thus, amino acids are the correct choice when discussing the foundational components of proteins.