What is the basic building block of proteins?

The basic building block of proteins is the amino acid. Proteins are polymers made up of long chains of amino acids linked together by peptide bonds. Each amino acid consists of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) that determines the specific properties of each amino acid.

In the context of protein synthesis, amino acids are assembled in specific sequences to form proteins, which are essential for various biological functions, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, providing structure to cells, and transporting molecules. There are 20 different amino acids that can be combined in various ways to create a vast array of proteins, each with unique functions and characteristics.

The other choices represent other types of biological molecules but do not relate to proteins in the same fundamental way as amino acids do. Nucleotides are the building blocks of nucleic acids like DNA and RNA, fatty acids are components of lipids, and nucleosides are similar to nucleotides but lack a phosphate group. Thus, amino acids are uniquely critical as the fundamental units that construct proteins.